I don't have any HP scanners, so I can't test it, but using nm and gvimdiff to compare libnetsnmp.so.30.0.2 and libnetsnmp.so.30.0.3 symbols shows that the former exports memdup and the new one doesn't but all other symbols are covered. I checked libsane.so.1 with nm and it isn't looking for memdup so I believe we're safe.
In the future, is there any sort of tool that I could do a reverse dependency lookup, i.e. "what extensions depend on this?"