so im getting the alien models from ghosts and if i replace the dog model with the alien model would it work?

Only if the dog model and the alien model share the same joint structure. And even then the alien will run like a dog... so no.

I can tell you the joints dont match. I actually rigged 2 alien models with the dog rig for someone. You'll have to weight the skin to the skeleton  (thanks WhippyTrout for showing me!) But like trem said they still run like dogs, so.. http://youtu.be/V-RmRkDwI0E