If those DOffs are currently on an assignment then they won't budge. Took me a little while to figure that out, so maybe that's the issue you're seeing.
It's possible, but I'm fairly sure they weren't assigned. The sort of mission they'd get used on, I don't chance Whites since they usually die faster than Mitt Romney at an NAACP meeting.
If your Doff is a fleet/base Doff, it can't be used in a project, and no, I have no way of knowing how to identify which is which.
While that is a user posting that, I did find from the dev's that everything is working as intended. In other words, certain Doffs you get from starbases will not work as contributable Doffs. I have encountered this myself, and it is frustrating.