The two Galactica series occur in the same continuity.
Anders and his resistance group can't have been the only people who survived on the Colonies. The survivors gradually managed to rebuild their civilization until they were attacked by the original-series Cylons (who were created by a non-human race, as stated in the series) and went on an exodus of their own to find Earth.
The two Galactica series are alternate continuities of each other.Battlestar Galactica (1978)
is the universe where the Colonials never created the cylons (however they do have the technology to do so - hence Muffet the robot dog). Instead of creating robots to fight their wars, their technological development focused on laser weapons.
"Alien" aliens exist in the classic universe, and don't in the reimagined universe. Also, the classic universe has colonies - lost and otherwise - where humans still exist.
Sire Uri never made it off Carillion.
Which is why he doesn't appear in the rest of the series. He was captured by the Ovions, and just as they were "preparing him for storage", the planet blew up.
- Gee, the idea of that being true would just break my heart.