It's a bit late to suggest this, but I'd like to seriously question if we really need Arimo. What's it's greatest benefit here? Is it more usable, readable etc. when compared to "web-safe" alternatives or is it purely a visual thing?
Personally I can't see anything being so great about it, not even that visual part, but what I can see is a pile of issues. I prefer my fonts to load fast and be readable, that's all, and at the moment I feel that neither of those has improved (quite the opposite really) in this new admin theme.
To summarize this, it just seems questionable to me if Arimo is really worth it. I can't see any real benefits, but then again, I'm not the typography guru here either
(Note: having to rely on a very slow mobile connection for a while has definitely affected my opinion, as you can see from the attached screenshot. That's not even funny anymore and I've been seeing it a lot lately. Not saying that it's a typical situation, but it's not unheard of either.)