For Fe-I i found 3 4-fold axis. which, even if there is more, suffices to know that there will be no EFG felt by these nuclei.
For Fe-IIa I found there to be 3 2-fold axis so this would not allow for an axially symmetric EFG, so eta will be different from 0 and the energy scheme of this nucleus will experience a lot of hyperfine splitting due to the EFG.
For Fe-IIb i found 2 2-fold axis and 1 4-fold axis this will allow for a axially symmetric EFG but the EFG will be present.