@Derelict:
You can't use 10.0.0.0/8 and 10.X.X.X/16. those subnets conflict.
facepalms Doh, I knew I forgot something. I've given the non-VLAN'd LAN 10.0.0.0/16 and left the rest as it was, and tweaked the config on the switch itself so it has the right net mask.
Anyways, weird discovery: Apparently there was a static DHCP assignment that got added for the client system and somehow THAT broke VLAN routing of information. Either that, or dhclient decided to go and break itself. It looks like the issue might've been related to that, because now data's being routed correctly. shrugs