I was under the impression that RSE RNG was quite difficult, especially when the battery's dry. Is it learnable in a short space of time?
On retail cartridge it is rather difficult, but it's probably easier than 4th or 5th on emulator (just time consuming). It's actually easier when the battery is dry to RNG (not that it matters for emerald, I think the seed is always 0). It's rather opinion based on whether or not it's easy, but if you have a few spare hours it wouldn't be hard to learn it.
If you want to try RNG on cart, make sure to go for a spread that is early on so you don't have to leave your DS (or gameboy) open for hours on end (the frames are advanced by time; around 60 per second, and since synchronizers don't work on stationaries... to give you an idea, the earlier flawless special attacker spread is timid on frame 105,404,008).