As of now I can't find a way to detect whether a collection has FTS enabled or not. Indexes are not shown on the indexes() API. In a multi environment context, we usually want to implement a fallback implementation using another text search option when FTS is not available (dev or staging env for instance).
By not having an API to know if it's available or not, you can throw $searchBeta functions in a pipeline on cluster without FTS. It won't fail but you'll get no results. You cannot differentiate that from a true empty result set.