LOL.  They certainly won't earn any merits with the garbage they spew, but their accounts are fully able to get and receive them from any other means.

OP, I'm curious as to why you're asking this.  The answer is no, there's not an option to have an account with merits disabled but I'm not sure why in the world you'd want something like that.

That's the only way I can see it happening, and who knows, Theymos might actually do it.  Seems pretty silly to me, though.