Nein, es ist nicht verboten!
Actually, it's a viable method for me, because I get into my chemical darkrooom only every few months. Scans are a way of exploring one's negatives. As Jovo said, you shouldn't later try to replicate in the darkroom what you did with the scan digitally. On the other hand, the digital print's materiality will be mediocre compared to a good FB chemical print. But we were talking contact sheets, I digress.
No 135 filing sheet fits into the scanning area of my 8x10 scanner, though.