I do not think that the custom definition is ok, not sure how ooh323 channel is named after the call is set, but I think that /$OUTNUM should be stripped. You wlll have to make a manual definition for it, or add a channel string in fop2 buttons you can try with something like:
[OOH323/TRUNKNAME] type=trunk label=OOH323-trunk queuecontext=from-queue privacy=none
or just add OOH323/TRUNKNAME in the channel field in fop2 buttons. To know what channel name to use, do a "core show channels" in the asterisk cli when you make a call, and remove the -SESSIONID suffix from the names you see there.