There are no Tibetan Mahayana monks in terms of Vinaya, as there is no
Mahayana or Vajrayana Vinaya -- they all follow the Mula-sarvastivadin
Vinaya. But as you surmise, not all robe-wearing Tibetans are monks
(Tibetan lay people understand who is who), though I imagine the ones shown
in Tricycle were actually monks. Not sure what the MS Vinaya says about
roller-coasters -- a good metaphor for Samsara, perhaps.