To be honest, it completely depends on what part of welcome week you mean and which university you'll be attending. If you were thinking more of the freshers week events, most student events only require you to have a valid ID to gain entry. I've had friends from other universities come and visit me and we went on nights out together so you'll be absolutely fine as long as you have a student ID. If you mean their course welcome week sessions, I would say no. That's their chance to get to know their new coursemates and some of those sessions take a register to see who's shown up and who hasn't. If you mean things like the campus tours and fairs at the uni then absolutely if that makes them feel more comfortable, sure go for it. Some sports and societies fairs require you to show/scan your student ID before you go so you may not get into those sorts of events.
Hope this helped!
Lucy - Digital Student Ambassador SHU