The pictus cats will eat any fish small enough to fit into their mouths, usually, but a betta should be too big. You could well be right about the activity levels, though - don't do it unless your betta has plenty of hiding spaces. Tall stem plants and floating plants will make him more comfortable, and a ZooMed betta log may not be a bad idea.
As for other tankmates, harlequin rasboras might work. Hopefully they'd be too big to fit in the cats' mouths, but they are pretty gentle fish and shouldn't bother your betta. Larger tetras, such as rummynose or black phantom could work, as may cherry or gold barbs (as long as they are in a big school to eliminate nipping). :)