Personally I think the Squamata are ideal - love them.
And as they come with guns as well, they have the chance to lead an armed insurrection if they don't get a decent pay deal! 
Right now the squamata are the only group that seems to have potential as an actual team of sorts. I might sprinkle in the occasional non-"union" type into the mix, just for flavor.

Or, instead of being fellow miners, the humans might be the overseers. They better not provoke "an armed insurrection" like you said, or they'd be toast.
Dan