Is the local hostname a data point that can be collected by WiFi access points after connecting to them similar to how MAC addresses can be collected?
Most certainly, however WiFi itself is nothing more than a network bridge between clients. Hostnames are send in by protocols that operate on top of LAN, for example DHCP, and are no different than connections over an ethernet cable.
MAC addresses are sent in the ethernet layer, even when there is no connection, for example to identify neighbors, or to send probes. If your device is setup to connect to any open network, the router could catch the hostname from the DHCP request. Keep in mind that a MAC address might prove more usefull when it comes to device identification.