No I don't believe so. The BDO is run by Lees and West, but it's possible they could negotiate with Dainty (or anyone else) with regards to certain bands if they were interested in putting them on the bill. They also like to include a majorly influential artist on every line-up if possible, which is why you will see people like Billy Bragg, Patti Smith, Iggy Pop, New Order etc. on there. Iron Maiden influenced a lot of kids that grew up in the 80s and went onto play in bands, plus they just did a bunch of sold out shows, but it depends on what sort of a feel they get. How much of a draw would Maiden actually be? It's pretty likely they wouldn't do it unless they headlined, and if there's a question about their "relevance" to a Big Day Out audience then they wouldn't be offered that.
On the subject of the BDO itself, it was always an awesome day whenever I went along. The last time I actually went to one was in 99, and that was mainly because a chick I wanted to nail was going and asked if I was going too, and I said "Yes" and then went and bought a ticket. I had almost zero interest in any of the bands except Cryogenic and Bodyjar whom I could have seen any weekend of the year, but I ended up having an awesome time. Seriously, if you like music, the Big Day Out is a killer event. Of all the ones I went to, the only band I hated was Shonen Knife (because they were just shit) and even some other bands I wasn't that into I enjoyed watching.