It's better to get it sorted out before you fly. Then you may be able to find out which hotel you are getting.
Since they have the highway it's quicker to get to Colombo city. Though once you reach Colombo you may get the traffic. It's boring at Jetwing in Negumbo. If it's just over 8 hours it's ok but if you get an evening it's better to go to Colombo. I have always asked before I travel and depending on the class you can get a good hotel in the city.
UL has just had a change in management and I have not flown after that so things may have changed.