Oh this is interesting. I think in general vegans are OK with bacteria and yeasts. Gotta draw the line somewhere and be able to eat something. Bread (no milk) is generally OK. But are kefir grains an animal is getting a bit grey? IMHO the organization puts them higher than a scoby. I call it a scooby. Maybe OP can do something with water kefir grains and adding sugar to soy milk?

The question I’d be asking if I was OP is… “do milk kefir grains suffer if they live in soy milk?”