It is not standard operating procedure, and demos wouldn't be done with production data. In fact, most enterprises would have contracts in place with Snowflake that explictly state that Snowflake staff can not be granted access to their Snowflake accounts (this is actually the default in the Snowflake enterprise professional services contract now).

You can understand it: Snowflake lawyers are naturally reluctant to have their staff be granted access to any customer's accounts.

It is however quite common to have Snowflake PS guys have limited access to customer dev environments.

However, such access, even in dev, should always be network restricted.