1:1 should support an alpha. I’m not sure why it isn’t. Have you tried Use Existing then Invert Existing for your alpha interpretation?
For faster imports, about the only way you’ll get a fast import is to have them render to the Avid DNxHD 220 codec. As you know, however, it doesn’t support alpha channels.
So…
If your graphics department can/will, have them render the movie, then render the alpha (matte). Import both into your Avid, cut your fill in, alpha on a video track above it, collapse them together and drop a Matte Key effect on top (don’t Alt+Drop it, just drop it on top). If you want, open your effect editor and hold Alt+Drag (or Alt+Ctrl+Drag–not in front of the system right now) the effect icon to your bin. It will save your Matte Key effect with source, thereby giving you a clip of your animation with alpha that you load into your source monitor.
This will take more render time on their end, but you’ll have fast import for both the matte and fill, then you just have to take a few seconds to combine them in your Avid and save the effect with source. If they’ll work with you on this, that’s how I’d go.
Otherwise, you’re going to be stuck with longer import times. I can’t think of another way around it.
Good luck, and let us know what you do.
Michael.