Well its true that many people do teach here without work visas (illegal) it doesnt really
mean anything they are married to locals. In itself that doesn't help a person or make
them any more 'untouchable' than anyone else.

Those not related to Chinese citizens and teaching without work visas are at a huge disadvantage. Non-work visas/RPs lasting for more than 3 months a time are very hard to obtain these days unless you are related to a Chinese ctizen, in which case you can get a 6 month RP without a medical check. If you wish a 1 year RP, you'll need to take a medical. However, such RPs do not allow you to teach legally. Yet they are long enough to make it worthwhile in terms of your pay and perks to teach in China. That's an important advantage of being related to a Chinese national.

However, the stiff penalties introduced a couple of years ago for those caught teaching illegally should be seriously considered. Of course, they apply to all foreigners, be they married to Chinese or not. Is it worth taking a chance and be fined heavily and banished for 3 years if you are found out? I don't think it is. Besides which, a 3 month L for touring means you will lose out on air fare allowance and vacation pay if you are not related to a Chinese national.

A very rich foreign teacher wed to a Chinese who wouldn't mind returning to his homeland with his Chinese spouse if he/she was forced to do so might well teach illegally. That is the only exception to not teaching legally in China that would make sense these days.