IMHO, any recommendation from somebody that has not known you personally for a length of time and/or has never flown with you is not worth the electrons. In fact, it could create the opposite of the desired effect when UAL calls the person to confirm the details of their relationship to you and the ruse is exposed.

But....nothing says letters have to be internal. Well written letters from your superiors, your FOs, or others you have flown with can be valuable---not to mention from those outside of aviation that can provide a positive indication of your character.

p.s. Unless you really want/need to repatriate, IMHO, you are nuts to seek employment at UAL considering your age and experience. But so long as you know what you are getting into, good luck with the process!!!