NEC originally billed Super Star Soldier as a "follow up" to Blazing Lazers in America because BL was one of their very few "successful" games here. It was the same notion that was behind the dubbing of Ankoku Densetsu as "The Legendary Axe II" here.
That being said, Tatsujin is correct: Gunhed/BL is not part of the Star Soldier series. Sure, you can catch similar sound effects here and boss cameos there if you compare one with the other, but while those may represent reverential "nods," they in no way make Gunhed a member of the SS series. After all, Gunhed shares far more in common with Super Aleste/Space Megaforce, right down to the "field thunder" armament, than it does with any Soldier game. It could be said just as easily, then, that Gunhed belongs to the Aleste series (a more easily supportable assertion since Compile was also behind that particular series and so many elements were similar between the games involved, from gameplay style to weaponry).
Anyway, Gunhed/BL is a standalone effort--not quite an Aleste game and certainly not a Star Soldier episode.