YAAC can operate over any TCP/IP network (including AREDN mesh). However, its only operating mode there is connecting to an APRS-IS server (or something that acts like an APRS-IS server). So, you could run a couple copies of javAPRSsrvr or aprsc on nodes of your AREDN network as a redundant "backbone" (basically, a scaled-down version of the APRS-IS Tier 1 and Tier 2 networks), and have all your YAAC (or other) APRS clients connect to them and both transmit and receive APRS packets using the APRS-IS server-client protocol.
YAAC can also function as an I-gate to relay traffic between RF and TCP/IP networks; other applications do a better job than YAAC at this task because YAAC was optimized for presenting data to its local operator, rather than for forwarding to other operators (aprx is an example of the other extreme of optimization), but YAAC can do it.
Hope this helps.
Andrew, KA2DDO
author of YAAC