While it's not possible to add MIBs directly into SolarWinds yourself. You can submit a case with SolarWinds support, send them the MIB files and request they be added to the MIB database. This is usually updated every 2 weeks I believe. While the addition of the MIBs doesn't mean SolarWinds will begin polling for that information, it does make it a bit easier to search for OIDs you want to monitor by having them in the updated MIB database you can get from the customer portal. This makes created Universal Pollers a bit easier.
Regards,
Matthew Harvey
Loop1 Systems