What are the potential pitfalls of putting a PhD on hold to be employed by the university?
I don't know your field, so my answer might be wrong.

It seems to me that taking this opportunity runs the risk of a small lifetime earnings hit (since there's a good chance that it means you would spend an extra year at PD salary rather than TT or industry salary), but that beyond that it would only help you career-wise.  Especially since this year wouldn't count against your clock.  That is, compared to your peers graduating at the same time as you, you'll have more experience, more publications, and experience with more projects.