Hi Martijn!
I too looked for a way to handle tapes returned from the vault without
operator replies, but I haven't found it.
You can use the following command if you are using a 3.1.2.1 server:

move drmedia * wherestate=vaultretrieve tostate=onsiteretrieve cmd="&vol"
cmdfilename="/whateverpath/checkin.txt"

Then you can issue a:

checkin libvol 3575lib status=scratch search=bulk
vollist=file://whateverpath/checkin.txt

This will still generate a operator reply, but it's only one reply for all
the tapes in the bulk I/O area and this way ADSM checks if the correct tapes
are being checked in. If you do it like you are doing now (using checkin
with search=bulk and no volume list) it is possible to check in a tape which
doesn't have the vaultretrieve status.
Kindest regards,
Eric van Loon