The problem is not artists being screwed over pay & benefits, the problem is that most VFX shops are struggling to stay in the black, period. In part this is due to overseas competition and expensive bidding processes, but also shops taking on work at or below cost in an effort to keep people employed.
There's zero chance of requiring studios to only use unionized VFX shops, so unionizing them will simply make them either less competitive (need to charge more to cover guaranteed benefits) or more prone to bankruptcy (cannot meet commitments to workers if there's a shortage of work)
What I'm pointing out is that having VFX shops crumble under financial pressure from studios doesn't do the studios any good either. Ultimately it's not about the hardware or software, but about the skill of the people using it. Given that R&H is a leader in its field and still went down, something is wrong with the business model.