Some do, some don't, sure. Google STT for example supports class tokens natively. There are also services like uniMRCP that allow for certain SRGS grammar features to be used with Google STT, but they are limited in what constructs they support. I've worked pretty extensively with a platform called Verbio, and they fully support the SRGS grammar specification. I work in conversational AI, and when I do implementations, I have to evaluate the complexity of the use case and whether or not a full grammar will be needed and choose a STT provider based on that.