Yes. Ethernet (including Gigabit Ethernet) is galvanic isolated by design and this both for copper and optical media.
- No current leaks
- No ground loops
Warning: Moving to optical doesn't really change much with respect to galvanic isolation, but it removes the possibility to power the unit via PoE which actually brings additional advantages whenever the unit is used to receive or drive unbalanced signals.
Whereas USB does NOT offer any galvanic isolation by design!
And even more importantly, USB is limited to lengths of max. 3 meters by design, while Ethernet (copper) is guaranteed to operate up to 100 meters while optical can be run over several kilometers.