Hi Peter,
UB15.10 is supported in MLNX_OFED and so does iSER.
As Sopie mentioned there is a need to add support to iSER target (ib_isert) for this platform as mentioned in the release notes.
TGT is a user space target and I've tried it (on MLNX_OFED-3.3 rc - but it shouldn't matter) and it works for me.
please supply more info on the TGT failures (+ all the steps you made) and I'll try to help.
thanks,
Max.
Storage Team.