I wanted to post my results of using United gift registry. I had done a test $75 GR charge back on Jan 8. After reading this thread I hadn't expected it to work since it sounded like it didn't for a lot of folks. Weeks passed and I didn't see any credit, and I figured it was dead. Then today I went and looked in my account and found, to my surprise, that 1/24 I did indeed have a "Travel Fee Rebate" credit of $75!
So it seems like the United Gift Registry isn't dead after all! I'll go ahead and make more deposits there to check the limit, like I did last year.
And to respond to another question, I also checked my Clear membership and it looks like mine got renewed through the end of 2017 so that seems active as well.