What the title says. Are they creeps only or can you play a mirelurk colony against someone’s survivors?
Creatures are possible in Battle Mode, though you may need to use have a non-creature leader and use the Creature Controller Leader Perk.
Wouldn’t make sense for the Mirelurk Queen to need a leader, but ok.
I think the idea is for them to have a creature controller to direct them tactically, rather than animalistic instinct. For solo/narrative play they can just go with AI directions to represent instinctive actions, but competitive play includes a human mind making strategic choices, represented on the board with a creature controller.
Just my two cents as to reasoning behind it 
Mirelurks are supposed to be intelligent enough to use tactics. It’d be fun to have a “mirelurk colony” equivalent of a settlement for campaign play.