I have a guy who asked me to trap some raccoons off his property but he also has a few cats that he does not want caught in the traps. My question is will dog proof traps keep the cats out or should I just avoid trapping this area?

I think if you use sweet bait you are less likely to catch kitties. Marshmallows and a sweet lure to back up.

Make sure you only use a pull trigger because cats will get caught in push pull triggers

Both of the above. Pull trigger and a sweet bait. That should cut your chances on non targets way, way down.

You’ll catch plenty in pull only triggers. Guaranteed.
Stay away from the fishy baits will help, but no guarantee lol.
“Curiosity killed the cat”

I’ve caught cats with marshmallows in pull triggers and it’s just cat nature if you observe a barn cat they will go by a hole and reach in it a lot of times . My Tom cat has got slapped numerous times in a weasel box baited with corn for chipmunks by a rat trap lol but cats in dp’s are not numerous but will happen. Depends how bad he wants coons gone , in my area people will release a cat over coons killing chickens etc.

Cage traps are the only safe option. DP's should not be set where they will be encountered by pets, cats or dogs. No matter the bait or the style of triggering system.

Use corn, no cats.

I remember my first DP cat was in a Duffer. Talk about an unpleasant surprise……

Who can argue with that. Certainly not anyone who has deer feeders out.

I use corn out of necessity…anything else and I have an ant bed.