I think the silver $'s would be too nippy for a betta.

I have silver dollars. Both were a decent size (would fit nicely on a piece of toast) I have never noticed any nippy tendencies. Mine have always been very peaceful with other fish. Has anybody experienced this?

bettas can live safely in a community setup. the main issue to address is probably water flow. bettas are very slow swimmers and can be a little unhappy if there is to much water flow.If you drop him in just see how he does at first. if he is struggling not to be sucked away then water flow should be adjusted.(aquaclear filters are great for this with the adjustable flow feature).however sometimes you can slow waterflow by putting a plant or rocks in front of
your filter. the only fish you should worry about doing harm to the betta is probably the clown loach. personally i wouldnt keep a loach and betta together, but plec and silverdollars should be fine.

Is it because of the switchblades that clown loaches keep under their eyes? I would have thought clown loaches would be pretty benign other than their built-in .007 weapons. But perhaps when the betta goes looking for a 'house' to hang out and the C.L. takes exception to his choice...

Actually, all fish mentioned tend to hide, so providing plants and shale, etc... would be a great help toward their respective sanities.