"If the police suspected a given service person of a crime, it would normally be much easier for them to take a fresh sample under their existing powers."
There are two possibilities.
1. They have a suspect.
2. They don't have a suspect.
It is 2, that will become the dominant mechanism for achieving 1 in years to come.
In fact this is the whole reason we're going to such great lengths to get so many people on the register now. The more people we have, the easier it will be to find suspects.
What could be easier than "Select * from PotentialCriminals PC Inner Join CrimeProfiles CP on CP.Profile = PC.Profile Where CP.Crime = 'HackneyShooting3rdDecember2008'"?
However, I support the DNA database, I think it's a brilliant idea, because it means thousands of men don't get done for rape because some hungover bird doesn't like the look of them in a line up.
The real reason servicemen won't have to worry about the police having it, is because most of them will have been tested as kids, long before they even thought of the army.