Firstly I wanted to make one thing clear: you will not have a nice, clean, easy-to-drag-your-butt ground for you to use to create space: you might be wearing tighter jeans, or have a backpack, or thick winter jacket; it might be dark, wet ground, or too near a wall... This means that not always you will be able to execute the drills you have been practising, which is when you would need to count on improvisation and unpredictability.
Although BJJ proved to be really effective on a one to one (even "no rules" duels), on the streets the situation is very different: his friends might kick my head, he might pull a knife, the police might arrive and take us both... So the last place I want to be is scrambling on the ground with someone. Whatever escape/defense I try to pull, I will do so bearing in mind that what I ultimately want is to stand up, rather than trying to sweep him, or anything like that. I probably would not pull full guard, for instance; instead I would try and move from under the person to create space so that I can push his hips away with my feet.
Foul Techniques and Context
I would never go for a groin grab. This is small target (not bring funny) and fairly easy to protect. One of the early UFCs had an episode like that, but instead of grabbing, they were punches. He was hitting the guy right on the balls, several times; no result. Biting, yes, but it would depend on timing and context. Look at nature, how lions hunt. They run behind their preys, usually take a first bite on their backs so they can secure their claws into their preys' skin, until they climb reaching a bite to the neck.
Neck control is very important in BJJ sport because that's how you control the whole of person's body, especially if you have their hips secure as well. Plus, strong bite to the neck can be fatal. If you can get your mouth near your aggressor's neck, you can rip their throats out. What about a stone? Stones are fantastic, either if I am trying to escape and all of the sudden I see a stone lying around there that I can grab and hit him from the bottom, or even if I am on the top and I wanted to finish him (in a very extreme case, as I do have consideration for human life; but if it were a much more serious situation I would definitely make use of it). Thus, in the same way that a triangle choke is only applicable depending on timing and context the same applies for what you are calling 'foul techniques'.
Timing: When to Make Use of Foul Techniques
Another key aspect to bear in mind is timing. If we are both standing in mid-range and he is launching a double-leg takedown, I would not try to aim my finger to his eye, but counter with a punch, for example, or more likely sprawl. If he already got me on side control but not fully locked, then I would not waste my time with foul techniques, as this extra time spent in trying to poke his eye would impede me from escaping and I would end up spending more time on the ground, which is against my principle of not staying on the ground. If, on another hand, the guy got me fully locked in this position, then that's when I would do a bit of bridging, and if that was too tight, then I would probably try to reach to the next available foul technique target.
Why Bother with Foul Techniques
Because simply put, there is nothing your attacker on top cannot do while you are biting, or eye poking him that he cannot do if you were not biting him; to the contrary: the longer you stay on the bottom, the more exposed you become. I shall expand it further.
Bottom Targets While you are on the bottom you might potentially be exposed to:
- getting choked, strangled - in other words, passing out;
- getting hit (a punch, stab, kick, knee, elbow, bullet, etc) by the guy on top;
- getting hit (a punch, stab, kick, knee, elbow, bullet, etc) by a different person;
- being bitten by the guy on top.
The attack vectors are virtually the same, whether you are biting, screaming or starting to create space to get out of the bottom - once the space has been created, then yes, his attack vectors are reduced. However, until such time, you are exposed to the same threats. What this means, essentially, is that you have a certain spectrum's width of risk (the types of attacks that can be launched against you from the top) which accommodate a certain number of escapes and counter you can perform. Adding foul techniques is an extra set of tools you could potentially add at no extra cost, meaning you are still exposed to the same threats as you would be if you had not considered foul techniques at all. So why not consider them?
Finally, as a double benefit, by incorporating these extra repertoire that most of orthodox MA trained people do not expect, you would also add the benefit of unpredictability and shock: usually under a sudden moment of surprise and shock, the natural reaction is to back away from the source of the unexpected event, which might be another window of opportunity for you to escape.
Foul Techniques are only labelled 'foul' because they are illegal in sports competition. This distinction does not exist on the streets, which is why for me they are like any other well-thought and practised technique that need to be mastered: self-preservation comes first.
Final Edit on Escalatin Issue
"Are you worried at all about potentially escalating the fight while in a disadvantageous position?"
Worrying about this would mean stop reacting in the hope that the aggressor will suddenly calm down and let go of me. In no way this is realistic. The more you comply, the harder it becomes for you to escape.