For both full scale and models, snap rolls can be done in any direction, not just horizontal, although most texts tend to describe a basic snap roll as a full power horizontal spin.

You will also find that most RC models fly differently and are not set up the same as full scale planes. Virtually all full scale planes will do an accelerated stall, but it is a rare (except for 3D) RC model that will do an accelerated stall. The reason is, you can not tell the approach to a stall in a model, feel the burble, so to speak. For this reason, most all models are set up to do a tight loop or turn at full up elevator rather than enter an accelerated stall.

The lack of an accelerated stall is why we normally use ailerons to help start the rotation and a lot of rudder for snaps. (I was watching the world acro champs one year on TV and noticed those pilots use aileron in snaps like we do. It helps keep them on line.) You may also find that many models will barrel roll for a half to 3/4 of a turn before breaking into a snap. This also makes them hard to stop on a heading unless the wings are very light (no inertia).