Yes, there are quite a few non-British pilots at Virgin. Among others, there are French, German, Australian, Iraqi, New Zealander, US, South African and Bajan. There may well be one or more Indian pilots. As in any EU-based JAA airline, you may work here if you have the right to live and work in the EU, and you have the relevent JAA or CAA qualifications, and such further qualification (hours/types) that Virgin may demand.
To answer your second question fully, I need more information about exactly from what perspective you're asking. Is your question related to your first point? Are you wondering if a pilot's nationality and his aircraft's country of registration are related? (Not necessarily) Or are you asking a more general question about what qualifications are required to fly given aircraft types?