I think it could be possible. Milkshape (a modeling program I use extensively) can inport Half-life models and export them pretty easily, but you need to find the plugins to make it possible.
I know this is possible because I saw a few guys on this board a couple of years ago able to export SFC models to HW so I'm almost certain it can work the other way around.
Also, don't listen to that crap your hearing from Sierra about threatening lawsuits. Just BS. Same thing happened to Ghost with his SFB stuff. Parmount threated to sue him if he didn't take down his stuff, but legally, as long as you don't sell the models, their is nothing Sierra can do.
Trust me, I know this to be a fact because the copyright laws can only do so much. If you don't beleive me, just check out this site and read up on US law...
http://www.copyright.gov/faq.html