Welcome joemans.
Theoretically, Podium should be able to send MIDI messages and parameter control to iDrum, regardless of whether it is in an instrument or fx slot. iDrum should also defer to the host (Podium’s) tempo.
If tracks in iDrum are mapped to their own MIDI channels, you should be able to have control over them with Podium.
Before getting ahead of myself, may I suggest you read through the MULTITIMBRAL & MULTIPLE IO PLUGINS section in the guide to ensure you’ve configured the plugin correctly.
Also, have a look at some of the videos collated here to see demonstrations.
I apologise for not installing iDrum and giving you a more definitive answer. Thing is, my toolkit is already more than sufficient, and I loathe to be on yet another developer’s mailing list.
That said, iDrum appears to be a powerful multi-sampler!