Regarding just the safety procedures training, I'm pretty sure something like that can be done using a video or online lesson CMs can access from home and do prior to returning. I mean, if it's good enough for kids to learn this way at home now, it should be good enough for
Disneyland CMs.
The ride specific training they obviously need to be on site for.
ETA: My kids are returning to school on Thursday and they have an online video and "quiz" they have to pass before they can come back.