Well, to clarify, Blastoice EX is not legal for tournaments. Only sets from Holon Phantoms and beyond are legal.
But yes, pokemon from different sets can evolve into each other. This also applies to "delta pokemon" or pokemon with a "{d}" on there cards. For example, and Ralts from Secret Wonders can evolve into a Kirlia from Dragon Frontiers, and that Kirlia can evolve into a Gardevoir from Secret Wonders as well.
But, mind you, there are some exceptions.
Pokemon with an owner in there name (ie, Team Aqua, Team Magma, Team Rocket, Brock's, Misty's, etc) can't evolve into a pokemon that isn't the same way. Ie, Team Aqua's Sealeo can't evolve into a Walrein MT. Likewise, Sealeo MT can't evolve into Team Aqua's Walrein.
This rule also applies to pokemon with "dark" in it's name. Ie, Dark Pupitar can't evolve into Tyranitar MT. Likewise, Pupitar MT can't evolve into Dark Tyranitar.
