HP gas compression is the main bottleneck of some of our fields. To be able to do production forecast for facility constraints, do we have to import GasLift data explicitly?

Yes, you should add the real GasLift data, as it is according to your production. When setting up constraints for the gas lift, you can set this up on Assets properties for Gas lift curves. You can use a linear curve which is used generically for all gas lift curves in your forecast, or you may alter the gas line curves minimum and maximum values.