Figured out a temporary work-around upon discovering that DAE files are plantext so "yay I can use vi to do my 3D modelling!" or rather I can edit it to temporarily rename the UV name to something shorter. So that now works. Also my complaining about the inverted UV map looks to be a bit of a red herring in practice as, although the image is upside-down in Blender, it effectively reinverts it on output so it looks fine in game. It just makes editing a bit fiddly.
One thing that continues to confound me is that the mesh is no longer coming out smooth once Blender's had its hands on it: it looks like I've done a "faces->set solid" and no amount of attempting to get smooth outlines (set smooth, auto smooth, convert to quads etc) will make any difference. A bit of Googling suggests this is likely a problem with Blender's export function so I'm not sure if there's anything the Exporter can do about it, but if there's any suggestions... Edit: actually, remove doubles fixed it. Probably obvious to everyone else, so everyone else is welcome to lol at the noob.
