I have the 6d and Nexus 7. I have used the eos remote app to view and take shots with the 6d. Compatibility is great. It just works! hope that helps.
It does :-), though I'm wondering why Canon writes that it isn't guaranteed to work - maybe they only test it on phones and/or the non-adapting resolution is the reason.
Android is open source and device manufactures modify the OS, sometimes significantly (e.g. Kindle Fire), for their own uses. It's an unfortunate consequence of open source, that it creates conflict issues. Canon is just covering their butts, any third-party manufacturer would do the same. One of the pluses to open source, is that if there was a conflict on a popular Android platform you can pretty much guarantee that developers would be on it ASAP. Go poke your nose in at XDA developers, those guys writing patches to stuff before the average user even knows it's a problem.
I've been working on flashing a custom ROM to my Kindle Fire HD for awhile now just so I could tether it to my camera. Looks like the 6D may fix that.
I work for a company that develops mobile apps and I can tell you that keeping up with new Android hardware and software forks from device manufacturers really keeps our engineers busy. iOS is much more predictable since only one company is messing with the code. As Skirball says, Canon is just protecting themselves.
Nothing against Android (I have an SIII), developing for it is just complicated. It makes me thankful that I only have to deal with the art side of things.