In some cases it's true though. Like on albums like BC&SL where the band writes the music and then James comes in to do the vocals later. There are lots of times where the vocals seem like a clear afterthought in DT.
Well, I'm not gonna comment on BC&SL, because it's one of my least favorite of their albums. Second least favorite, actually.
But to say that JLB is a "permanent hired gun" is just plain disrespectful. He's the front man for the band, not just in terms of singing the songs, but being the face and the voice of the band. And sure, there was a time when Portnoy just wanted to do ALL the speaking on behalf of the band, at interviews and such, but hey, if you asked me, I would've said that wasn't right anyway.
As soon as Portnoy was gone, JLB really stepped up as the frontman for the band though. He's been doing more interviews, and informing everyone about what's going on in the band.
And again, albums like BCSL aside, most of DT's discography showcase JLB's vocal capabilities really well. His range has always been amazing, and even in hard times, when his voice was at its worst, he still had insane vocal capabilities, and for a band which prides itself on being an all around fantastic group of musicians, masters of their craft, JLB easily fits into that category, and is an integral part of what makes Dream Theater complete.