Tomtom has a good track record with handsfree on HTC devices, so I'd bet the Droid Eris should be no problem. Still, you should test/confirm, just walk into a Verizon store with your Rider and ask them to test with a live model.
PLUS services won't work. The Droid Eris (and all Android devices to date) do not support Bluetooth DUN for data. Bluetooth DUN is required for PLUS services.