Yes it plays them Multiview, see my screenshot above, probably you don't have the right Datatypes.
Anyway now there is a new version of AmiTube v05 that also allows you to download Youtube Videos in MPG1 format (better quality) where you can use FFPlay to view them.
A few days ago I asked the developer if it was possible for AmiTube to download other video formats, I asked if it was possible to download videos without conversion or in the original format Youtube MP4, in this way always thanks to FFPlay you could enjoy more quality videos.