I've cleaned my Romanian Tokarev with simple green before. Just checked under the grip panels, and there's no rust to be found.
A few caveats, though.
I spritzed on a diluted solution, then after a brief scrub with a toothbrush, I immediately rinsed it under off with generous amount of hot tap water. The simple green didn't stay on the metal for more than maybe a minute. After the individual parts (field strip) were clean, I rinsed under boiling water, and dried the parts off using a rag and a can of compressed air. After the gun was completely dry, I put a light coat of oil over every surface I could. I also live in a very dry climate, so any remaining moisture that might have missed would have quickly evaporated.
Regardless, I don't see the need for regular cleaning using simple green. I used it on my Tokarev because I had shot an exceptional amount of corrosive surplus in it, and it had a small amount of factory cosmoline in it. My CZ83 could probably use it, but that's also surplus. The main advantage I see in cleaning using simple green is primarily as a non-toxic (to my knowledge) alternative to non-chlorinated brake cleaner or gun scrubber in that it strips almost all oils and grease off the surface of the gun, but unlike brake cleaner it won't melt my contact to my eye if some makes it passed my safety goggles.
It's a decent carbon remover if you scrub enough, but it's a fantastic degreaser.