Help With Betta Fish?

I have a community tank with neon tetras, red platies, black and silver mollies, glofish, pleco, octos, cory cats, and a guppy female. You think a Betta would be ok or would it kill my fish. I tried to get all fish that are not fin nippers. Its a 29 gallon high with excellent filtration. I do water changes so im not worried bout water quality. You think the betta would be ok in there. Also I purchased a few cardinal tetras but they are scraping themselves on the driftwood and gravel but they only seem to do it after they eat. I see no white spots on them and purchased some parasite clear tank tablets but they are still doing it. I raised the temp, I always add salt since i have black molly's. What could this be? cause now my panda cory's are doing it. But its only after they eat...