To address the last part first:
You can have any new MIB's included by submitting them to SW via either email to firstname.lastname@example.org or submitting them to http://solarwinds.leapfile.com to the email address support@solarwinds.NET (Notice the emphasized .net).
Someone in SW adds them in and rebuilds the MIB database weekly, usually by Wednesday of the next week, you can download a new MIBs.cfg.
Now.. having to copy it to more places than Program Files\SolarWinds\Common is still a pisser, I have to copy it into 3 places for access to the Toolset, NCM, and NPM. SW *really* needs to fix that, 1.5GB for MIBs is not just ridiculous, it's ridonkulous..
To add a +1 to the request to have it walk the non-standard MIBs for any recognized vendor type (Adtran, AcmePacket, Juniper to name just a few) would be a huge plus, that I hadn't crafted a request for yet, but had been planning to for at least the last 60 days..
This is something we are actively looking at how to best address going forward