Oh hell no. She's second to main character.
In terms of character hierarchy, it's in this order: Alucard, Seras, Integra, Walter, Anderson, Major, Pip, and the rest are rather minor. Pip's almost minor actually, but he does some seriously awesome shit and is very close to Seras.
Like 40% of Hellsing is about Seras.
But the thing is, her biggest scene hasn't been animated yet so she's still somewhat minor in fandom. When OVA5 comes out she'll definitely be more popular.
I mean, nobody talked about Schrodinger and Rip Van Winkle before OVA4, you'd think nobody cared. Now they're everywhere.