no it isn't illegal to play Pokemon hacks but hacking the game is illegal
not to my knowledge
There are gba rom hacks with diamond and pearl Pokemon.
It would only be illegal if the hacks were being sold for profit, which they aren't. So no, they aren't illegal. Enjoy your hacks.
Pokemon hacks are legal. it is site hacking which would be "illegal" Pokemon Quartz is a hacked game. Yes they are legal and if you are planning on making a game to put on the internet, then you need to know the Format and Game Codes before you do so
Yes
it would matter what you are using to play it
Video game "hacks" are bootleg versions of actual games that have been recreated with certain alterations. There are a vast array of Pokemon hacks, but some notable ones include Pokemon Adventure, Pokemon Brown, and Pokemon Prism.
Pokemon Shiny Gold, Pokemon Naranja/Orange, Pokemon Prism, etc. You can find more information about hacks on bulbapedia.
go suck it
POKEMON
Apparently it is, which is illegal. So don't do it. WA does not endorse illegal actions.
Officially, no. But there are some fan games/ROM hacks that have you play as Team Rocket; some good examples are Pokemon: Team Rocket Edition (a hack of Red) and Pokemon Rocket Strike (a hack of FireRed).