As far as we know... He's suggested to be Evil, with Hydaelyn being suggested as Good.

By the nature of how Hydaelyn caused the fracturing of the world into the 13 shards in order to lock Zodiark away. In addition to how she also helps adventurers such as the WoL deal with Primals that would threaten the world(s) by granting the Echo.

Though, it's unclear if Zodiark can also grant the Echo (If he cannot, then it leads to some awkward realization involving the fact that Ascians became Ascians due to the Echo enabling them to do so)

So, we have Ascians trying to rejoin all the shards with the Source - Not only ending all life on the shard, but also causing a Calamity on the Source. With the purpose of reviving Zodiark. Which suggests some level of Evil, because of the extreme loss of life involved in this.

Then we have Hydaelyn who's doing things like expending her life essence to grant a Hero the Blessing of Light so that they may protect the world (Soon to be worlds) as well as things like saving Minfilia's soul from disappearing into the Aethereal Sea (Though, one could argue this in of itself, is an act of Evil... ). This suggests a level of benevolence and thus Good.

It's possible that Shadowbringers might complicate things somewhat, but I think at the base level, Zodiark being Evil and Hydaelyn being Good are very likely to be absolutes.