I'll just reiterate what others have ( rightfully ) said and then close this.
EA designed the SF unlocks to be used only in vanilla BF2. THere is no way around that. No one knows why they did it. It is fair to assume their intention was to make people buy the expansion. If you want to play the new weaponry in SF, you ned to play on the team that has them, SEALs or SAS.
If you have unlocks left, you can use them to unlock SF weapons for BF2 ( provided you already have unlocked the BF2 weapon for that kit ). That's it.
Thanks to everyone who provided links or directed towards the search function
closed.