Yes, it's completely seamless - in fact I understand FoV was supposed to be part of the original game, but the publishers didn't give them time to finish it (hence its initial release as an expansion pack).
But the original ED+FoV is not compatible with the remastered DKS - if you bought DKS hoping to continue from an original ED game, you're out of luck, and you'll have to either start a new FoV character or start from scratch and replay the remastered ED component of DKS.
EDIT: I realise from the previous topic that I might have confused you about the issue. There are two version of 'ED + Fov' - the original, and the DKS (remastered). Both versions allow you to continue your game without interruption, but the two versions aren't compatable. So you'll only have problems if you try mixing save-games from the 'original' ED/FoV with the 'remastered' DKS version.
Sorry if I gave you the wrong idea...