Most of the ones I go against are ones that are pokesaved with nicknames on battle revoltion in random. My nickname legit Pokemon don't have their nicknames show and I pretty sure someone said pokesave Pokemon nicknames show on battle revolution. Though I'm not 100% sure.....
Unless, you know, check that little box that verifies that's the Pokemon's nickname. Then it'll show up as normal on PBR. >_>
You have to be careful with this thoguh. I thought my shiny floatzel was hacked cause it kept the name "MUSTEFLOTT" on random wifi...
Then only recently I realized why, it's french XD
Oh yeah, as for legends in masterballs. Celebi, Jirachi, and Manaphy can only be found in normal pokeballs, save for TRU manaphy, as far as I know. This also applies for starters obviously, and lucario, as you only get those as starters or eggs.
The foreign Pokemon rule only applies if Pokemon were Pal Parked via same region Pal Park (German to German, not English to Japanese GBA to Japanese DP or the like), or of course caught in that region with no nickname.
As for the event Pokemon, Mew and Jirachi also appeared in Cherish Balls at the PALCITY and 2007 Tanabata event respectively. Lucario can be in a Cherish Ball as it is also another PALCITY event.