DashieXP has gamer tags under the names Dashie and DashieXP on Xbox 360.
You can bet that, with the amount of money he's making from all the attention surrounding him, he can afford to have multiple Xbox Live accounts, and probably even multiple consoles if he wanted to!
I've also seen him on PSN (Playstation Network) as DashieXp too - so it's a gamertag he's stuck to across platforms.
He must have reserved those DashieXp gamertags before he got famous, because now there are dozens of fake spinoffs going by names which are very similar to his.
He's one of the most popular gamers on the world of Xbox though, and I wonder if that has anything to do with the "XP" in his gamertag.
Xbox is owned by Microsoft after all, and XP was part of the name of Microsoft's well known software Windows XP.