I basically do the same thing with two Expresses in my house (using a Time Capsule as a main router) and it works perfectly.I've tried this before with the Express, it doesn't work.
One Express is in the living room and bridges to a ethernet-only TiVo. The other one is in my housemate's room and bridges to a switch that he has his ethernet-only desktop and his ethernet-only TiVo plugged into.
Both work perfectly because they're transparent to the ethernet devices.