What FW version you have on the HUB shouldn’t matter because you are accessing the HUB as a network share (basically like a NAS).
However, one reason that you may not be seeing the coverart is if you are using the .png/.jpg extension trick for your covers. Unfortunately, this does not work on the SMP and if your covers were originally a .png, then you will not see the covers displayed.
Also, instead of accessing the HUB as a network share, I would suggest that you add folder(s) that you want as a Medial Library Share. Setup / System / Media Library / Media Library Manager for Network Share / Add network share to Media Library. Then set your content source (red button on remote) to My Media Library.
I would also suggest that if you are going to use the same theme on both and you want both to work together, you should flash the latest FW version on the HUB (because the latest HUB and SMP version work the same). Then, take the Mojo version you downloaded from the SMP forum, open the Mojo folder and copy it’s content and paste it to the Mojo theme folder on the HUB.
Just remember though, that you can’t use the .png/.jpg trick on the SMP. So you also need to download the coverbox template found on the SMP Mojo thread and use it to generate .jpgs (instead of .pngs) for your coverboxes.