Yes, my guess is that that tall, bearded man in the clip is Bernie Vickers, who joined the Watersons briefly when they re-formed in 1972, after Norma returned from working in Monserrat. (John was presumably still down south, where he'd gone to study with Sligo fiddler Michael Gorman, after the group disbanded in 1968, though he eventually resettled in Hull.) Vickers was soon displaced by Martin Carthy, Norma's new husband, who was recruited in the summer of 1972, but considering Carthy's many projects around that time, Vickers may have continued to sing with the Watersons for a while yet when Carthy wasn't available. A photo of the Watersons with this bearded gent appears in the Mighty River booklet just at the point where Vickers' involvement with the Watersons is mentioned, though in general the photos don't correlate closely with the text. I'm pretty sure John's not the man in the clip, given his appearance in the documentary and in the Mighty River booklet photos (including one where he's bearded).