Well, for me it's a yes and a no. Being an instrumentalist in an ensemble definitely has helped me in a million ways musically (including composition) and it's doubtful I would have the inspiration to compose without the appreciation and understanding what is means to come together and produce music. In terms of the actual process, I have had little passion for noodling/improvising on a instrument outside of piano (and I can barely play one) - it's probably because solo playing has never appealing to me, and whenever I'm playing alone I almost always envisioning the ensemble sound as I play.
Additionally, the things I want from my music right now barely align with what I've heard and experienced in ensembles (clarinet player, so largely wind bands) and I find myself questioning if what I already know how to write is what I actually want to be writing. I didn't realize it until recently, but I think in some ways being an instrumentalist has impeded my composition as well as helped it, in this respect.