re: FBI, 5 other agencies probe possible covert Kremlin aid to Trump

Absolutely it counts as evidence. I would point out that the dossier gives a timeframe for the Prague meeting as occurring in August of 2016 (FYI another's article actually extended this timeframe into September as well). So a witness saying he definitely was in California one day in August doesn't do much to prove he wasn't in Prague any other day that month. So it's shitty evidence.