I've heard native and very-long-time BVI residents say 'Joss' Van Dyke, so I think there's some ambiguity on pronunciation.
I chartered for many years before I moved to Tortola and always coached my crew to properly pronounce it as 'Yost' Van Dyke. I think that's the correct German/Dutch pronunciation of Joost Van Dyk that the island was named for. Now that I'm here, I see that everyone here pronounces it as 'Jost' or 'Joss'.
