I've looked around on Nicovideo and Pixiv for stuff related to the games, and supposedly the UGSF "saga" continuity branches out to more than just Starblade and Galaxian^3...it's apparently been around since the original Galaxian. Other games that are supposedly part of this continuity include Baraduke, Nebulasray, and Star Luster. I'm guessing the UGSF has multiple factions that each specialize in various areas.
The continuity between the games is furthered by the fact that Star Ixiom on PlayStation has the Gaia from Star Luster and the GeoSword from Starblade in it, and I think Zolgear is an enemy in one mission!
