I have to admit that I haven't examined the belly of an alpha carefully to see what's under there. But most trainers have at least 3/32 balsa sheeting on the belly and a ply crutch fuse, possibly some open bays as well. All covered with heatshrink, and that's more than strong enogh for belly landing. To be honest though, I wouldn't take the gear off unless I was landing in tall grass or cut grass with no rocks, etc. and if I had nicly cut and cleared grass, you wouldn't need to handlaunch. But I've been places where the field was totally unimproved, lots of waist high grass. We could (and did) fly from it if you threw everything and belly landed in the grass. Landing gear got in the way in that case, and would snag and create problems. So it has a more to do with the local conditions than anything.

Generally, I wouldn't hand launch or belly land a trainer unless I had a good reason for it, and only if the local conditions made sense. But if the conditions warrented it, I wouldn't hesitate to do it either. YMMV.