Theoretically the mixer (transformers, diodes) should be balanced and whether you ground pin 2 or pin 5 makes no difference, especially within the specified working range (0.5-500MHz). However, realistically you might get different LO leakage on the RF and IF ports, but that is over -50dBc on both ports at HF so not really something to worry about. Look at the Isolation L-R and Isolation L-I in the ADE1 datasheet, the values are slightly different:
Cheers,
Razvan.
