I'm pretty sure as long as you've got your DM10 set for midi passthrough, and the keyboard is using a different channel for output, your vst(s) will see them separately. I've got my DM10X midi'd into Addictive Drums, and I've installed the Addictive Keys demo and we have a Yamaha keyboard with midi out, I'll try to test this theory.. I just wonder if a) my pc has enough memory to process all that and b) if I'm even able to run two vst progs at the same time on the one pc (assuming I've got enough ram and hd space etc, I'm not sure if XLN Addictive products will run simultaneously on the same machine but worth checking). Now I'm wondering if I can run them both, plus fire up my Ableton recording software and see if both the drums and the keyboards are loadable into midi tracks.
On the other hand, if you're using the newer midi usb connections, you could plug both the keys and the drums into your computer directly and not have to piggyback.. but I use an audio interface with one midi input so I'd have to use the pass through option. Will let you know if I get a chance to test this idea. But yeah, should be doable