Based on the fine print on Chase's website, you should get miles as long as the merchant is recorded as United. Personally, I think I got the 2x miles when I bought some snacks on a flight, and that definitely was not a ticket purchase.
Earning Miles:
You, as the primary cardmember, will earn a total of 1 mile for each $1 of Net Purchases. You will earn an additional 1 mile for each $1 of Net Purchases (for a total of 2 miles) where United Airlines is identified as the merchant on your monthly credit card statement. Therefore, United purchases on some discount travel websites and on board will not qualify for the stated rewards offer. ("Net Purchases" are purchases of goods and services made by you or any authorized user on your account minus any returns or refunds, and do not include balance transfers, cash advances, cash-like charges such as travelers checks, foreign currency, and money orders, any checks that access your account, overdraft advances, interest, unauthorized or fraudulent charges, or fees of any kind, including an annual fee, if applicable.) There is no maximum number of miles that you can accumulate in the program. See Rewards Program Rules and Regulations, which will be mailed after your account is established.
Source:
https://creditcards.chase.com/credit...edit-card.aspx