Hello lets go through each product here
Neither product is going to create a thumbnail off of the video automatically as that requires a specialty server software that is not widely used yet. In Photopost you can upload a thumbnail to represent the multimedia file although in vbgallery you can not.
Both applications integrate with
vb 3.5.4 well the main difference being Photopost administration etc is within its own admin panel and vbgallery is within
vb admin panel since it is essentially an add on to
vb
vBGallery does not play multimedia files although there is a hack you can install. I am not sure whether its totally plugin based or file edits. Now Photopost Pro you can elect to play the video's inline so that when you click the thumbnail it will start playing the video and when done you go to the next video by clicking the next thumbnail.
As far as who can upload and who can comment both applications handle that through usergroup permissions.