Had no issues with taking photos on the platforms on the Moscow Metro in late May, this with an actual camera and a smartphone. To be honest, most of the locals there are just doing their day to day, so tend not to take much notice of you. Normally any staff were situated at the bottom of the escalators, rather than the platforms.
As for mainline trains, again don't seem to recall any issues with photos being taken (this at Leningradsky and Yaroslavskaya), the main difficulty is the large crowds on the platform getting in the way! Usually more train staff on the platform upon departure, and not so visible on arrival. Security is more prevalent (xray machines) for the Sapsan at Leningradsky, but the majority of the staff will speak English.
I think as long as you are not taking photos of police, or security staff there shouldn't be an issue.
