Hi,
I've had GERD since I was in my early 20's (maybe even earlier), but did not get Crohn's until around the age of 45. Over the years, I've had to take stronger and stronger anti-reflux medications, and now I'm on a proton-pump-inhibitor called Zegerid.
I recently had a small bowel resection due to severe stricturing of my terminal ileum, and for several months prior to my surgery, I noticed that my GERD was the worst it's ever been. I was even eating low residue, low fiber, and extremely bland foods, yet I still had severe problems. I even slept sitting up (in a recliner) for 5 months prior to my surgery.
Since my surgery for the stricturing, my GERD seems to have settled down somewhat, but I'm sure I'll be on PPIs for life.
So, a short answer is that I think a Crohn's flare can make GERD worse.