angels

Sure you can. I have three large Koi angels in with my pair of albino Kribs in a 110. Tank size and relative fish size will be the determining factors. Just don't expect any fry to survive with the angel around.

The krib parents will guard the fry. They will be able to keep them for 2 to 3 days once they are free swimming. After that the fry move around too much for the parents to guard them well enough. If you take the fry before then you will have no problems. This is actually what I do. I siphon the fry out once they leave their tank.

A simple rule of thumb with fish: If it can fit in the mouth it will be eaten. Yes congo's could eat the fry. For almost any fish if you intend on breeding and raising the fry the very best option is a tank to themselves. Anything else is just a risk. While I have one pair in with my angels I also have two other pairs in their own 20 gallon tanks. Best to keep them alone for the easiest way to raise the fry.

Now I had read somewhere (and I wish I remember where, but I think it was The Cichlid by M.E. Sweeney) that target fish are sometimes a good idea for breeding pairs of Cichlids (to maintain harmony by providing a conduit for behavioural displacement), but they should probably be something more expendable than Congos. Plus, I am not sure how aggressive Kribs get when breeding, so they might be okay without them, and, indeed, if they don't kill the target fish, said fish will snack on little Kribs.

ChilDawg, you are correct about dither fish. They are often used as you describe as well as being used to make really shy fish feel more comfortable. For Kribs though I find they are not needed. Also you want to size the dither fish according to the fish they will be going in with. Congos can get as big, perhaps bigger then Kribs. Something somewhat smaller would be much better. Myself I like to use fish that are just big enough not to be a meal for the prime fish as a dither. So for Kribs that would be something in the neon size range although I am not recomending neons. White clouds would be good. The exception here would be with very large very aggressive fish. Here you want something that can take it and dish it out but will not actively hunt down the small fish that are born in the tank. You also do not want the dither fish to compete with the prime fish for living spaces.