I tried but my VIN wasn't also recognized. It did say the VIN won't be in the database if you purchased the vehicles less than 60 days. And if you try the other method of putting in the Make and Model, the Enclave is not even listed. This tells me that this site is not as active as it should be. It's not GM's priority because not too many people are complaining enough.
OK, It recognized my VIN, asked for current mileage, avg miles driven per day/month, and then vehicle nickname. It then confirms the VIN and asks for Make/Model/Year. Enclave isn't an option so that's as far as I got.
I've had my Enclave for 6 weeks and mygmlink says my vin is a good vin number but not in the system yet and to try after 60 days of ownership. The OnStar site, on the other hand, has been sending me email links to my vehicle status from the get go. I guess OnStar being a paid service might have something to do with it.