Yes, and UA would be the only nonstop-flight option. But if the OP were willing to take connecting flights, redeeming SQ miles on AS (via SEA) would be cheaper. Redeeming BA Avios for AA (via PHX or LAX), or for AS (via SEA) would cost 40,000 Avios for each roundtrip in Coach. But, Amex occasionally runs generous bonuses for converting MR points to BA Avios, so that's a consideration, as is the fact that BA would not charge extra for stopping over for a day or more at the connecting city -- if that's of any interest to the OP.