Thats what it appears. West Ham are saying he's going to be at Upton Park http://www.whufc.com/articles/20121126/go-vip-for-chelsea-visit_2236884_2991894
The Evening Standard has been carrying an advert saying Allen will be at the West Ham match for a couple of weeks. It does not seem to have had too bad an effect on ticket sales.
Surely the Manager should be with the team on matchday and not at a paid event. I know it isn't a league game but it is still an important match and the fans are still paying money to see a competitive game so I would expect a strong line up including the Manager. The FA Cup is a great competition and I have always been a huge fan and would expect us to take it seriously especially when we are up against a team in the division above and looking for a cup upset. For MA not to be there to rather be at West Ham undermines the competition and doesn't look good to the players. I hope it is wrong and he was only provisionally booked prior to the Scunthorpe game on the chance we would not go through and he would be free this weekend. Well I will be in Preston even if MA isn't!!!
I would be very very surprised if MA was not with his team. These corporate events are book months in advance and usually with the caveat that 'should circumstances elsewhere preclude attendance' being included.
I would expect MA to be at Preston on Saturday with the team. I cannot say if that will happen, just my expectations of our manager.