Sam Adama was not a hero, much less a (possible) action hero. Are people thinking Sam Adama has already filled the quota for gay characters?
As I recall neither Alison Scagliotti nor Genelle Williams started as regulars. They needed someone to interact with at "home" with the characters, hence Lena. They needed someone to interact with Artie at the warehouse, hence Claudia. Then when they want to take Claudia out of the warehouse, they need a partner for her, since the show's centered first of all on the Pete/Myka pairing. Hence, they need Jinxy or someone. The credits are irrelevant at this point. (And they don't include Genelle Williams if I remember correctly. I tend to tune out credits unless I like the theme music.)
They've written that the character works there as an agent. That's main cast, no matter you spin it. The point is, if they are trying out the character to see if it works before they promote Ashmore to regular status and main cast, then not putting him in the episodes is pretty damn peculiar.
Jaime Murray may have had more screen time with one episode and her character is supposed to be in limbo or something!