Lots of the FLW guys fish the BASS Open events that are local to them whenever their schedules allow it (same even goes with the BASS professionals as well). Winning an Open event qualifies you to fish the Bassmaster Classic. Plus, you can win some money while doing it and it could be good practice if it's a body of water that your circuit fishes.
But to touch on your point, yes, these can be a gateway into BASS Elite's for the FLW guys. Lots of big names from the FLW Tour have jumped over the Elites in recent years (Wheeler, Daniels Jr, Lefebre, etc, etc).