Hi, you can definitely use ITensor dmrg for this kind of Hamiltonian, as I did in a project a while back (see http://arxiv.org/abs/1104.5493 ).
A key step is that you must set the "ConserveNf" option to false when creating the "sites" site set object.
See here: http://itensor.org/docs.cgi?page=classes/spinless
for documentation on the Spinless site set and
for documentation on the Hubbard (fermions with spin) site set.
With these, and with the correct signs defining your Hamiltonian (remember that inside of AutoMPO the C and Cdag operators do anticommute), you should be able to use AutoMPO and dmrg just fine.
Please let me know if this doesn't fix your issue and I can take a look at your code if needed.