I don't think you can load just any MIB into Solarwinds. I believe they need to have that MIB file and incorporate it into their common MIB.CFG file. From what I've read they are very accommadating to get these integrated quickly into Orion if you provide the MIB file.
However, I notice they already have some Atrica MIBs and I would think you could use Orion's Universal Device Poller to discover your devices and build Top-n reports from these custom pollers. If you haven't used the Universal Device Poller it's a journey for sure, but you'll figure it out in no time. I think they have a short video online to get you started.
Yea, I just starting using Solarwinds a few days ago so I'm trying to make it all work! I will try this out on Monday and hopefully I can get some of the reports working the way I need.