We are interested in the MT3334SMI for a special application and the requirement is different from a standard modem in that there isn't any DC voltage over the line (dry line). Does this modem support leased lines?

Yes, it does support 'dry line' operation, but it does not support lease-line operation.

However, these models support both 2-wire lease-line operation and will work over dry lines:

MT5634SMI-92
MT5634SMI-P-92
MT5634SMI-IP