Plugin (Instrument VST) Compatibility & Panning

[Brozilla]

Recently I had purchased the EWQL Hollywood Orchestra Diamond and waiting for the package.
Since this uses (IIRC) the Play VST would it work with OpenMPT? Would assume so and honestly it's best to try it out but maybe someone knows beforehand?

Also I don't seem to be able to use the panning (volume slides, Dxx, seem to not work but velocity commands do.) Right now I'm reading and assume we use the Zxx MIDI Macro or PC (Parameter Control) for midi changes? Currently in investigation and assume this is the case. Some commands (e.g vibrato) do work and I'm experimenting as to what can be done using traditional .it commands.
For submission I'd (obviously) need to sample the instruments but would like to work with an "as is" sound first.

[Saga Musix]

Yes, Play should work just fine in OpenMPT.
Panning is not sent to plugins because there is no standardized (and no per-note) way of doing so. You will have to figure out which MIDI CC or plugin parameter (if any) can control panning - quite often CC 10 is used for panning, as prescribed in the General MIDI standard. This affects all notes on the same MIDI channel.
The same is true about volume by the way, hence there are various settings to handle those (read up on "Volume Command Handling" in the instrument tab).
Hopefully volume and panning will become more easy to control in the future using per-instrument macros (that is, macros that are automatically called when there is a panning or volume command in a pattern). Some initial code for this has been lying around for a while, but I have yet to find a straight-forward and intuitive way to offer these settings to the user without crowding the UI even more.

(Vibrato is done using pitch bend, which is somewhat standardized since it's a dedicated MIDI command, but it's only per MIDI channel, so if more than one note plays on a MIDI channel, all of them are affected. And OpenMPT cannot know the pitch bend depth of the plugin, so the user has to enter it manually.)

[Brozilla]

Midi Macros seem to be taking care of the plugin specific stuff like you mentioned (panning.)
Just need to work with it a bit more so thanks for the help!