I too am seeing this issue and have been seeing it for a couple of months. Seems like Wi-Fi calls on iPhones are showing up consistently but Androids are inconsistent or altogether missing.
I have tested this on 7010 and 7220 controllers running both 6.5.0.1 and 6.5.0.4. The two Android phones I have to test with are a Droid Turbo and a Nexus 5 both with current 6.0.1 OS release.
I have tried calls of 1-2 mins as well as 5-10 mins and neither shows up.
On a side note I was told we also could not see Skype 4 Business cloud calls on the dashboard or in AMP but I am onsite with a customer now who is using cloud hosted Skype 4 Business and we are seeing their calls. No difference in ArubaOS versions or AMON settings as I used the same script to enable AMON on both controllers.
There seems to be some inconsistency with the UCC info that is being presented.