I disagree with TeaMonkey's comments about commercial use of Dynamo, because - as you've pointed out - it's been done with a very successful game.
Just because it's suitable for one game to use it, it doesn't mean it's suitable for any game to use it. In the case of BlitzMax you'll need to create a wrapper of some sort to use the library and there are associated licencing issues with that.
I've just downloaded the demo for Breakquest and after a cursory glance it looks like it's in breach of the LGPL - no copy of the LGPL licence, no source code or linkable object library in the distribution?
Also, DynaMo's written in C++. Best to stick with a plain C library if possible for ease of integration.
But Will's right. If it's just for 2D physics there's no point using a 3D engine as a 3D engine will be far more complex than a 2D one. The internals of a 2D physics engine will be completely different to those of a 3D one.