I believe the whole SIN-MAN-IAH routing will carry a codeshare from UA.
For UA, it's a win win. They have been deliberating what to do to add MAN capacity, whether it was a 2nd EWR or new route to ORD.
This new MAN-IAH route offers that chance to add capacity and serve that capacity through Houston, also adding a new route possibility to the UA potential.
Of course it's been very strongly suggested that Newark will gain the B767-300 next summer, so, after years of stagnation from UA at MAN for a few years, next year sees a sudden jolt of acivity.