First on the rodent traps. Yes, definitely you are permitted to use snap traps and any other kinds of traps in all areas of restaurants. Your considerations should be these. In dining areas you absolutely do not want patrons of the restaurant seeing a trap or even worse a trap with a rodent in it. When we eat in a restaurant we prefer to divorce ourselves from the idea that our chosen restaurant could possibly have a rodent problem, so keeping all traps out of sight and mind to the patrons is important. In the kitchen and other "Food Areas" of the restaurant the traps should be set so they cannot be contacted by anyone and will not be covered with food, hit with wash water, or otherwise contaminated or interfered with. Snap traps are considered a more humane trap than glue traps, and with either kind of trap the rodents captured should be disposed of quickly. 

A "Food Area" is defined as any place where food is prepared, processed, served, or stored. The dining areas are a "food area" when food is present, but a non-food area when no patrons are there and no food is on the tables. It is important to carefully read each Label of each product you use to determine what that particular product legally allows you to do in a food area, or even in a non-food area for that matter. Most residual products allow no more than a "spot" application in a food area, and may even be restricted to a crack and crevice application. Frankly, if it is roaches that you are concerned with a C&C application is going to be more effective anyhow, as this puts the active ingredient directly into where the roaches spend 80% of their time. Spraying generally over open surfaces is a waste of material, and coincidentally increases the chances of that spray contacting people or food. 

So, the Label tells you "where" you can spray in that restaurant and "how" you are allowed to make that application. There are very few places in a restaurant that you are prohibited from treating in any manner, but it is the method of application that is important. Treating in food preparation and cooking areas is perfectly acceptable if you determine that those are the locations where the roaches are to be found. Just as important in the long-term management of this problem in that restaurant , however, would be EXCLUSION. If this is a regular account that you visit every month or two months, and on each visit you re-apply your material into the same cracks and crevices, why not take just a moment longer on one trip, fill in that crevice with the appropriate caulking, and never have to treat it again? Roaches cannot hide where they cannot squeeze in. It really should be our Hippocratic Oath to use as little toxin as possible and still achieve the best roach control we can, and eliminating harborage is a big step in that direction. 

You do seem to distinguish between "spraying" and "crack and crevice", so it appears that you are currently treating within the food areas, and that C&C application should be fine and effective. Even in the dining area you would be better off, for roach control, to do C&C applications rather than spraying along baseboards and other open surfaces. It is simple math that it takes contact TIME between the roach and the active ingredient in order to get sufficient a.i. into the roach to kill it, and a quick run across your band sprays is not likely to get that contact time. Applying insecticides onto exposed surfaces is also putting that a.i. where it is much more likely to degrade rapidly.