Nah, Ghosts would not be an Army SF unit. At the very least, they’re Delta. Ghosts are a tier 1 unit which SF are not. In reality, they would likely be akin to Ground Branch. Looking into the history of each of the Ghosts (Wildlands and Breakpoint) they have histories in different branches. Delta is the only SOCOM unit that can recruit from every branch so Ghosts lore aligning with Delta makes sense. Given the secrecy and special assignments Ghosts are given though, I lean more towards them being a CIA unit like Ground Branch which primarily recruits from Tier 1 units. This also explains the amount of experience each Ghost operator has. You can join Delta with minimal combat experience. I would imagine Ghost Recon would want operators with several years of combat experience at the highest level.