a) Yes, I got several calls, and in between collecting the 5th and 6th egg, I flew to Kanto to catch a Slugma for Flame Body (and it took me a long time to find one). I thought that nothing was proven to advance the IRNG other than collecting eggs, though?
b) No; if you enter the cave and proceed as if you were going to fight Red, it's the first outdoor area. There's no Hail there. As far as I know, it's the ONLY place to catch level 50+ non-legendary Pokémon in the game.
precisely... nothing has been proven... and there are many things we have yet to test... it is very possible (and probably likely) that something advanced it unexpectedly....