Pex is able to handle higher temperatures (aka hot water) than conventional PE (only cold water) so it should handle the friction built up heat from repeated rowing. Did you use Type A, B, or C Pex (All Pex's meet the same criteria but they are all made slightly differently)? A is the best and would look equivalent to your average bushing and would probably stand up the best. I'm also curious how a 1/2" wirsbo/uponor ring would stand up (used for their Pex system) size wise to the 5/8" oar lock shaft. I'm gonna try later today lol.
15' AIRE Wave Destroyer - MadCatr Frame - Sawyer MXS oars w/Duramax blades