Right now we only have plugins for exporting our custom XML format from Blender. This plugin is written in plaintext python scripts though so someone else could port it to Maya if they tried.
For now, yes you could model stuff in Maya then just do the vertex group assignments in Blender. Though you could probably assign the vertex groups on Maya too (if it has a concept of that) as long as you're able to get it to Blender with those intact.
It doesn't matter if you use quads as long as it gets triangulated prior to putting it in the game (I believe our XML exporter does this or has an option for it).
And lastly, this game doesn't appear to have any limitations on polygon count. Or atleast it it does, they're quite high. As an example, someone here once created a car with more polygons than the first 3 levels of the game.