I have never had a problem using any of the *A Gold perks with my BD gold card.
- use of premium checkin desks
- use of lounges (for some agents it is the first time they've seen a bmi card)
- use of priority boarding on UA

Often I book my US domestic sectors as separate tickets as it's sometimes a lot cheaper to buy cheap Y fares separately than tacking them onto the international sectors where these were booked as J. (I know, I know, sometimes they can't/won't to interline, but on the way in you've got to collect your bag anyway and I prefer to bring it to the same terminal as I am departing from in order to recheck it - but at least it arrives at the same time as I do!)