For paid tickets upgraded by GUF2, then obviously that would have to be correct since the booking is done largely outwith BAEC's control. If they didn't do that, there would soon be a eBay style market for these e-vouchers! For Avios redemptions by BAEC, you can upgrade someone else if not in a HHA.

For HHA members, my understanding is that the booking has to be made by the person who gains it (unless under 18 years old) but it can be used for travel by someone else in the HHA - but travel by someone outside HHA is not allowed. A GUF2 can be a GUF1, you can do it on just a single trip for one person, or a return for one person. It is indeed the case that the summary texts around e-vouchers is possibly misleading in its terseness, the T&Cs are a better start point.