Simple, Scots in service of the Crown in the "British" forces become Mercenaries.
Look to Ireland for your answer.
With all due respect to that comment from Holly Beach Louisiana.
HM Forces personnel are not mercenaries. The UK armed forces includes personnel from across the Commonwealth as well as Ireland, and has done for years. There is no reason why that should not continue to some extent in the event of a 'Yes' vote in the referendum.
BTW I am not making a pro-independence point. But on this particular issue of the treatment of forces personnel in the event of independence, the White Paper proposals quoted by the OP are sensible, in so far as they go.