Homefront will indeed use THQ's "Online Pass" functionality, similar to the system used by EA for its sports games and co-opted by THQ for its UFC title last year. Players who buy the game new will get a code in the box to play online with, and anyone who buys the game with a used code will have to shell out an extra $10 for the full online experience. Not paying the money won't lock them out completely, but it will limit functionality to only level 5, rather than the full version's 75 levels of progression.
The single-player side of the game won't be affected by the online pass at all. It sounds like an interesting option -- certain players who don't care about progression might pass on paying the extra fee completely. We'll have to see how THQ's gamble goes over when the game arrives in March.