Yes, you can use the Ethernet Adapter with a USB hub; I've been doing it for quite awhile w/o incident...
i bought this one http://apple.ipod.produkte.gravis.d...USB-20-Kombo-Hub-inkl-Ethernet-Anschluss.html
small, all-in-one, 3 x usb; 1 x 10/100 ethernet; built specially for mba
yeah, I've bought it allready and its everytime in use with my mba. it's great because its all-in-one and because its tiny and because there is no nead for external power (but there is an option for external power-in).
In the end I recommend it.
i couldn't find that product here in the states for the life of me so I went ahead and ordered this one:
http://www.dlink.com/products/?pid=133