Though the conquest results show Windurst controlling the Elshimo Lowlands region and I was able to grab the supplies quest, the outpost is occupied by a San d'Oria flag bearer, who will not accept by supplies. I tried logging in and out but still the same elf.

Checked back today after maintenance and the Outpost has Gridanian NPCs. Woots!

Ehehehe you're in the wrong neighbourhood *grabs paddle*

Bad sentence on my part. The NPCs changed over to Grindanian folk in the Elshimo Lowlands Outpost. Must have fixed itself with the reboot of the instance from the morning maintenance.