I use T2 security for United all the time, especially since a good chunk of my flights on UAX leave from T2 anyway. However, last time I checked the United counter at T2 is not staffed, electronic kiosks only so if you need help getting a boarding pass or need to check a bag, you have to go to T1. Don't know if the skycaps will check United bags curbside at T2.

At times, the Pre-check line in T2 can back into the hall, but lately it seems like it has gotten better. YMMV.