The bell pepper and tomato are both Solanaceae/nightshade family plants just different genera (Capsicum and Solanum respectively), so I wouldn't expect poisonous peppers. That said, I'm not sure it's likely to have a very high survival rate being in different genera. Eggplant and tomato are both Solanum, might be interesting to try to graft those together. I think Capiscum is only peppers, so your best luck would probably be another pepper. I'll be interested to hear your results.

Got me curious, so I did some searching. I don't have an account to read the full text, but the abstract should give you a good idea.

Also found an interesting one on eggplant rootstock/tomato scion grafting in the Phillipines. Google 'graft eggplant tomato', should be the first link.

Here is a link that might be useful: Anatomy and physiology of graft incompatibility in solanaceous plants