In the "Uncertainty Report (Production)" in the Gas and Gas Lift tables, are the Gas tables the export gas? and if you add Gas + Gas Lift that is what is used for capacity constraint calculations?

Yes, the gas tables are the same as export gas (without considering gas lift). Regarding your second question, In the uncertainty report, if you add the gas and gas lift, you get the approximate total gas which is used for capacity constraint calculation. (Approximate because it is two different percentiles. They cannot be summed, since they are based on different combinations of realizations. But the sum will be very close to the values being constrained.