Definitely.

I do that to request my wife's upgrades when we pay for her ticket but I am on an award ticket (since paid and award have to be booked separately). Then they will request her upgrades and seat her next to me in a preferred seat, and allow both of us to check 2 bags (plus priority tag her bags).

I prefer to do all of this via twitter rather than calling in, and of course you have to check in at the counter for the linked PNRs to mean anything.