Mileage credit on discounted Y fare will definitely be 100% of flown miles on the UA codeshare; if flying on BD flight number (as I did) mileage credit should be the same. My mileage credit, in typical BD style, still hasn't come through some four weeks after the flight, despite several phone calls and submission of boarding cards/receipts.

Which is a same, because I need those miles to requalify. I've now got to beg to get seats in Y+ on my UA flight to San Diego this weekend.