Not dealing in absolutes, depending on whose opinion you get in HR on the day of the week in the second lunar year, everyone is correct in this thread to one degree or another. I've heard both stories!
Presently, IMO, HR tells you that they want you to have flown with the individual. It is ideal, nor absolute. Have submitted LOR's for folks I knew and had not flown with (one started the other day) as well as for those I flew with and started in other recent classes. OTOH, folks have been hired with none. On the whole the preference is (from pilots anyway, IMO)
1. LOR from UPS pilot (Line or management with reputation important for either referer) who has flown with you.
2. LOR from UPS pilot who knows you well, but hasn't flown with you (maybe same company or sister squadron, etc) and can vouch for your flying skills and work ethic, etc
3. LOR form pilot who does not know you well. Yes, HR takes these and the question is asked on how well you know the individual and if you have flown together.
Notes: My opinions only <again>.
a. An LOR from a UPS manager anywhere that knows you well is very useful (and has gotten interviews)
b. LOR's are likely used to confirm or deny HR's own assesment (reason folks with no LOR get hired)
c. If you DO know a Brown pilot and answer that you do in the interview, not having their LOR is a kiss of death. (If the person won't spend the 30 minutes online doing the form, you are not worth it in the HR mind (reasonable), the negative speaks volumes.)
d. Ask the Brown pilot if they need a copy of your resume to assist in the LOR, it refreshes my memory of when we flew together, etc.
Luck to all, so far I am personally batting a very good score, though everyone I have referred has had other LOR's besides mine, so am sure at the least I am not screwing them over
Also, everyone HR picked up has done well on the line/training and hasn't left UPS for other companies.