I think he is trying to glue bits of stuff down to acrylic sheets so it will stay put. I think it would work. This is no different than placing other artificial ornaments, you are just making a wider base for it.
Silicone or epoxy will work, depending on what you are gluing. <Silicone don't stick well to plexi, but if you use slate for your base, silicone would work well.> I wouldn't use hot glue ... doesn't stick under water.
80 gal FW with 30 gal DIY wet/dry/sump.
9 fancy golds, 1 hillstream loaches, 1 rubber-lip pleco (C. thomasi), 3 SAEs, small school of white cloud minnows, planted.