It's fairly early days for this board and we are not yet sure exactly how the software will pan out. This means the only honest answer I can give about the VPU is "I don't know".
The GPU story should be pretty much the same as Hikey since, like Hikey, the Poplar has a MALI GPU. These is an out-of-tree open source kernel driver which is paired with closed source MALI userspace code that implements OpenGL ES.
Again specifics on how OpenEmbedded BSP layers will be provided are not entirely clear at the moment. However the modular layered nature of OE should allow BSP layers to be cleanly separated form any proprietary RDK layers.