Not necessarily, there are several ways they could release a proprietary app: either code it from scratch so they own the copyright, use OSS code that has a commercial-friendly license (eg. MIT), use an OSS library that allows them to link with their proprietary code (eg. LGPL).
But even if they did release the source code, I think they could still be profitable. Their main customers would be people who want something that "just works", and a lot of those people would rather see a few ads than deal with downloading a modified version of the official client. People who hate ads and are willing to tinker are more likely to run their own insurance, IMO.