Hello John,
I don’t see why this should not be possible. Might need to increase exposure to get suitable SNR for fainter targets.
VSS observer David Conner has routinely used a 50mm finder for photometry. Lots of details and links to his articles in the VSS Circular on his website: https://davidsconner.weebly.com/. I can see he doing pre use photometry on EBs below mag 11. Also examples of using a Seestar S30.
Jeremy