Hmmm let's see here....
The idea of taking a Russian's place is a cool one...I would have never thought up something like that....it's like that James Bond move - Thunderball, was it? I can't remember. Anyway...
1. Methinks it would be better if you jumped right into the role of Spetznaz instead of a lowly rifle platoon leader. As a regular lieutenant you'd have no chance of getting the info you need until it's D-Day, and as an intelligence officer you'd have no chance of seeing combat, so stepping right into the shoes of a spetznaz trooper probably works best. You'd be involved in pre-invasion operations and stuff, so you'd most likely know ahead of time.
2. I'm still trying to think up a solid reason why you'd continue to fight NATO - I had something typed out and then found a hole in it, so I've got nothing. I mean, you could just make a run for it, or you could surrender to Americans at the first opportunity, or something like that. After all, you are an SF operator...you could easily cut and run if you wanted to, being trained in E&E.
Seems like you need something to motivate the player to do this...maybe NATO sends an SF team - not to pick you up, but to take you out so that they rid themselves of a problem - ie how to get you out, something like that. Maybe if you made that sniper attack happen before you started killing Americans, I dunno...maybe it would clear things up a bit.
Frankly I don't think it works to say that you have no choice but to attack US troops...you'd try to avoid that by any means you can, and when you think about it, your mission is done after you supplied the necessary info. To hell with hindering their war efforts - they don't need you to do that, or you could even just "desert" your new comrades and do it guerrilla-style.
Unfortunately it seems that the whole campaign hinges on one factor that doesn't stand up too well to scrutiny. If you could somehow strengthen that connection, then it could work.
Very creative...that one point kind of kills it for me though. I don't know if that's the prevailing sentiment, but again, I think it's a problem.