Happygran1964, 2020 has been a tough year and I'm sure many grandparents have been disappointed in the level of contact they have been able to have with their grandchildren. Maybe without that you'd have been able to visit in person more and it would never have been an issue?
I don't think you are unreasonable to say you'd like to Facetime but, other than expressing this wish, you can't enforce it. I have to say that I wouldn't be very inclined to organise Facetime with someone who wanted to Facetime with my infant. I'd have to do the work because a baby can't talk - and I don't like Facetime, so doing it under those circumstances would just be stressful. Maybe DIL feels overwhelmed with all the texts you say you send her? She's busy with a baby, after all.
You do get videos and photos so that is how your son wishes to communicate at this time. This isn't a DIL issue, this is about your son who has different preferred methods of communication with you than what you want. He's also autistic so he may find the communication side of things a bit harder than some, but that doesn't mean your DIL has to compensate for him by carrying his relationships.
As far as the other grandmother seeing the baby more because she isn't employed and you work with children, I don't think that's an excuse. My own mother isn't seeing my family at the moment because she works in a setting with children. That means she is exposed to a lot of people, so the risk of her bringing Covid into my home seems high. If she wasn't working in this setting, we would see her. It's not personal.
How were things before all this? Did you visit regularly? If all was more regular then, it might be that what you are missing at this time is one of the sad things that we have to ride out during this pandemic. You haven't been shut out as you are receiving photos and videos. The real issue may be that you and your son just have different ways you prefer to communicate.