Yes according to the FAQ:

"The WiFi fingerprints are also the same across all devices so that learning using one device is guaranteed to work across all devices."

https://github.com/schollz/find/blob/master/FAQ.md#doesnt-th...

I don't see why you couldn't. You're just shipping serial numbers through the air at that point.

devices have different antennas, in different places and with different orientation.

A wifi antenna should always be vertically oriented because radio waves are polarized, and if you aren't in line with the polarization you'll lose gain.

What is the polarity of ipad antenna on your lap? :) Then you have multipath (reflections). This is why wifi cards had diversity switch and two antennas even before MIMO, and with 11n gained spatial diversity and beamforming.

random google result: http://www.theruckusroom.net/2011/06/a-polarizing-problem.ht...

It's accurate over 1 metre squared. I don't think the placement is too large of an issue.

mismatched polarisation can lead to over 20db of attenuation

Yes you can! Just share the "Group" name that you used for the fingerprinting.