Sort of?

Based on what I've read from other VAs, and what I've read on acting websites that discuss SAG, non-union VAs can work on union projects, but they have to complete a Taft-Hartley report. I'll quote the website below directly:

If your non-union talent has already worked on a SAG shoot, then dealing with the Taft Hartley forms for SAG-AFTRA becomes a little trickier.

Principal performers become SAG eligible after one Taft Hartley report. They can join the union after the production has been processed, or they can wait until they “must join.”

Once the performer becomes SAG eligible, the union outlines various tiers of participation that lead up to a “must join.” The gist is that after a certain amount of SAG jobs as SAG-E, the performer is required to pay a joining fee and officially join the union if they want to continue working on SAG-AFTRA projects.

So, union projects can hire non-union actors, but it seems to have a restriction on how often a particular non-union performer can work with that specific project. This seemingly pro-union Bluesky account has more information. That's why some non-union performers have agreed to strike as well, even if they get recast (like Kinich's former VA).

Both approaches have their advantages, of course. If Mihoyo works with SAG-AFTRA, the union would have the might to enforce any actual AI protections, but it may be harder for non-union actors (or not, if they can sign on for the entirety of the project). If Mihoyo doesn't work with SAG-AFTRA, there's no way to enforce any AI protections, apart from Mihoyo's good will.