Well acording to Pokemon its not...
Basically the game bans legandary Pokemon from going inside building along side a few more big Pokemon. If I remember corectly then I dont think that wailord can go inside and I'm not superised
But as garydos is not a legandary, it can go inside and as regigigas is legandary, it cannot go inside
(I think there are a lot of spelling mistakes here XD)