Are non-standard aspect ratios supported with hardware H264 Decoding

I have an application playing back MP4 H264s through a mediaElement object.   The video it'll be playing back is a 5:2 aspect ratio and I'm trying to decide between playing 5:2 H264s or letterboxing 16:9 H264s.   Are hardware decoders able to play back non-standard aspect ratio MP4s or do they fail over to CPU for odd-ball sized MP4s?   Is there a way to debug and profile H264 decoding to ensure that it's utilizing DXVA?  I can see in the profiler that it's calling DirectX but whether or not it's being hardware decoded on the GPU or not is ambiguous. 

Thanks!