Deimos is one of Mektek's creations, so they'd probably need permission from them in order to put it in MWLL.
And as such we aren't even considering it. The discussion on that one pretty much ends right there. 
Errr... are you writing it off because you assume this, or because you know? Because it's a canon TRO 3085 mech, and I
seriously doubt MekTek still owns the rights to the art. I doubt Catalyst has to give MekTek royalties for every copy of the 3085 TRO sold, and I also doubt they'd even CONSIDER making it a canon mech unless they owned it.
Furthermore, what makes CBT assets 'free to use', but MekTek designs aren't? The TRO Hellhound/Conjurer is an Inner Sphere-looking pile of poop, but the MekTek design is the over-the-shoulder cannons, which I'm going to assume is the design you're using. So that design is okay to use, even though it's not in any TRO?
This doesn't sound right.