I agree with everyone else that you should tell people that you want to apply points for upgrades on their behalf.

One is that UA is constantly checking to make sure upgrades were not bought or sold--you don't want UA employees asking too many questions about your MileagePlus account.

Two is the risk of seats getting messed up. There's a lot of situations where I'd rather sit together in economy instead of apart in business.

Three is that applying upgrades could potentially mess up reservations, for example gate upgrades often split PNRs, even if all passengers end up getting upgraded. For an infrequent flier to deal with a split PNR could be really tough in any sort of IRROPS, especially if they don't know what happened.