Data point on 200$ credit - it's hit or miss. In December I used $170 worth on taxes/fees on a United award ticket. I ate up the $30 remainder with a United gift card. As I understand it, neither should qualify.
This year, I bought a $200 gift card outright. The charge apparently didn't come up as a "fee", so they declared they'd contact United to verify. I said I would find the receipt instead, but they indeed went back to my account and notated the fee as being based on an "e-gift," so no HUCB.
No worries on finding $200 in airline charges in the next 11 months, but gift cards (at least larger ones) are no panacea.
Blast!
-Jeff