Caveat: Some MWII vehicles, and Wartracks from MWII will not be available to use in Modern Warfare III.
Note: Challenges within MWII (e.g., Seasonal Prestige Challenges allowing Calling Cards to be unlocked) can be unlocked only in MWII, but unlocked Calling Cards (including those you go back and unlock in MWII) will carry forward.
Generally, no, aside from the following caveats:
Some vehicle Skins may not be available.
Wartracks will not carry forward.
Some Tactical and Lethal equipment may not be available depending on the removing of those items in MWIII, to be replaced with MWIII-only equipment.
Exact Tactical and Lethal equipment within MWIII will be revealed at a later date.
Otherwise, all this Modern Warfare II cosmetics will be usable in Modern Warfare III. However, as with Operators and Weapons, any cosmetic item with a limited time unlock won’t be available unless it was unlocked in MWII at the appropriate time.
COD MW3 Bot Lobby, Boosting, Accounts