1/2" may be too high for any toilet to sit flat on the floor, although you might have a better chance with the unifit adapter than with a normal toilet.
The unifit adapter uses a normal wax ring, but in your case, maybe a waxless seal might give a little more room - you'd have to try it to see. Both types are available at most big box home stores.
Drilling into concrete isn't bad with the right drill bit. It goes faster with a hammer drill, but for a few holes, a standard drill with a carbide concrete bit would work. You could use plastic anchors, lead anchors, or a special brand of screws called Tapcons. Each will require a specific hole - don't try to use either a bigger or smaller hole than the fastener calls for. The Tapcons are hardened steel that actually thread themselves into the concrete after you drill the pilot hole.
The Unifit adapter anchors to the existing flange, then near the rear of the toilet is another set of bolts that hold the toilet. That end of the adapter needs to be anchored to then hold the toilet, and that is where the extra screws go. The "normal" bolt holes just hold the front end and seal of the adapter in place.