Yes, the one problem though is booking a UA flight through AC, AC will not be willing to change your frequent flyer number. AC thinks changing frequent flyer number on award tickets is akin to fraud because their IT is incapable of distinguishing between award and revenue tickets for accrual.

Once you get your UA confirmation number, call UA and have them put your 1K number in to get upgraded on the award ticket, unless you're booking J. It's not guaranteed and a risk compared to booking directly trough MileagePlus.