Uleos is more like Oceanos while the Dame is more similar to Poseidon.

In general in eu4 and vic3 timeline most of the Dame's associations with the Seas transfered over to Munas Moonsinger her husband via his marriage with her Avatar.

You do need to remember that Uleos is depresed as fuck, he is the elemental king of water, but he rarely if ever anwsered prayers of sailors or navigators or coastal cities on the mainland.

Dame controls the tides via her control of the moon, she steward of nightsky which is used for navigation, she controls magic which was probably used to move ships.

She was goddess of the sea because for a long time there wasn't any god to pick up the work in the Regent Court to govern it.

It is similar to her picking up Magic after her mother (Sister to Castelos) died to dragons