Disruptor himself, or any hero for that matter, does not need '$alphatest 1' in their base .vmt (disruptor_color.vmt in this case, or more specifically mount_color.vmt) as long as you go ahead and add it to your own .vmt upon compiling.

mount_color.vmt does not have $alphatest 1 so be sure that when you go to compile your materials that you add it if you plan to use alpha cards for the spikes.

The concept looks great and I really look forward to seeing how the mesh turns out.