I never had a problem when I was 5-boxing in LOTRO. I had a kinmate raise a fuss once when I first started dual-boxing, but I quickly quashed that, since he was claiming I was botting.

When Carn Dum had the castle problem (couldn't zone into the Carn Dum castle) and I was regularly farming Rune of Winged Dominances, I had a number of CSRs come out to port me inside. One specifically asked me if there were 5 different people, or if someone was boxing, and I had a short conversation with her about me 5-boxing. She was taking screenshots of my 4 Dwarven RKs in their matching outfits (in different colors).