In my experience, Aruba 8320 (and thus I presume Aruba 8400 too) is able to be recognized by HPE IMC 7.3 E0605P06...as I already pointed out here the IMC is just able to monitor it (not the VSX!) without being able to recognize VSX (and VSX related LAGs, ISL and ISL Keep-alive links) and OoBM...indeed IMC Network Topology maps my Aruba 8320 VSX as two unconnected Aruba 8320 (this was described also here).
Another thing I'm not able to do with IMC is to backup Aruba 8320 configuration file even if the SNMPv3 connection between the IMC and both my Aruba 8320s is working.
For LLDP over OoBM read this.
Personally I found a little bit embarassing to see that both HPE IMC and Aruba AirWave can only monitor (not manage) the Aruba 8320/8400X...even if I suspect that AirWave is somewhat in a better position than IMC considering that Aruba developed Aruba NetEdit (who knows? maybe there will be soon a way to launch it from AirWave...) and that network monitoring is probably becoming an Aruba-Aruba affair only (they engineered Aruba 8320/8400X, they did the same for AirWave...HPE IMC is powerful...but - I suspect - it's not entirely under the control of Aruba development teams...at least up to now).