Injecting salt into PyCrypto KDF - useful?
Identical passwords will still get unique PBKDF2 hashes given a unique salt, regardless of which mechanism you use.

I don't think explicitly adding the salt improves the security of this scheme. The designer PBKDF2 have already considered and solved this problem. There is no need for you to try to duplicate their efforts. 

I think it's safer to use the well tested and well understood construction of PBKDF2:

dv = PBKDF2(password, salt)