vMotion and HA between different ESX versions

Is it possible to do HA *and* vMotion between:

1. Box A (ESX 4.1) and Box B (ESXi 4.1) 

2. Box A (ESX 4.1) and Box B (ESXi 4.1 Update 1)

3. Box A (ESX 4.1) and Box B (ESX 4.1 Update 1)

I can't remember if the underlying ESX OS needs to be indentical versions or hypervisors.?

Thanks