ARD does use VNC; you can also use a separate VNC server, such as OSXvnc, which performed better for me over WAN connections when I've compared the two (but that was some time ago, so Apple has likely improved their server in the meantime.)
ARD does use VNC; you can also use a separate VNC server, such as OSXvnc, which performed better for me over WAN connections when I've compared the two (but that was some time ago, so Apple has likely improved their server in the meantime.)