I would still be surprised if they didn't hire the cruise pilots for 4 reasons:
a) The main restriction of an airline is rules, regs, etc. Captains aren't in the greatest supply plus they cost a lot so you want to optimise their usefulness. A cruise pilot extends the duty time of the more critical to flight F/O and Capt. Where I currently work a crew of three can have a duty time of up to 15 hours and a crew of 4, 17 hours. As a result and correct me if I'm wrong anyone but potentially SJ's layover time may be reduced if they fly with cruise pilots to current destinations of NY and Dubai. (that may cause a whirlwind on this thread now)
b) You expose someone to the airline industry gently without having to worry about flying a 180k aircraft. Over the two years the cruise pilots will be assessed, maintained in sim landings and licences kept current. The airline can also determine, based on their performance and character how likely they are to be a strong asset in the future. You'd be niave to think any airline does not look at and grade its young pilots for future commands, their work ethic, look at their sickness', demeanour and how they interact with other employees. Silverjet would get to do this over 2 years and cherry pick.
c) Don't quote me but IATA brought in a reg back in September about flights over water at night and a need for a third pilot. North American to European NATS are primarilly an overnight jaunt.
d) When/if they do roll out new routes then they are able to hit the ground running. Plus basic for a FO is £47k and £27k for a cruise pilot.