I would google a plumber or a dentist so why not a therapist? It seems like due diligence, frankly, to use the most basic means at your disposal to check out a person who is performing an important service for you.

Clearly there's an element of curiosity and intensity with therapists that we rarely have with plumbers and dentists but this doesn't suddenly make it unkosher to google them. If you're not hacking, there's no boundary violation. If you feel uncomfortable looking, then don't. But that doesn't make it wrong.