Hi Bill,
I wrote the article you mentioned, so should hopefully be able to help you out!
When I wrote that post in March, I managed to get a secondary authorship rich snippet on a video result through what i could only pin down to tagging a G+ profile as the uploader element, in spite of Google saying that the uploader profile must be on the same domain. http://support.google.com/webmasters/bin/answer.py?hl=en&answer=80472#1
Since the flurry of updates earlier this year, this doesn't seem to work any more and indeed, It feels like Google are settling on only providing a single rich snippet for a given result - unless there is the added "+1'd by someone in your Google+ profiles". the standard Rel=author box has also been reduced in size and if you receive multiple results from the same site, then you seemingly now only get one result with authorship mark-up and then the remaining links below.
The main reason for my original recommendation was the possibility of a second rich snippet, with tha "mini-authorship" display which Google were seemingly offering at the time in conjunction with other snippets.
Since this has now seemingly been canned, the recommendation is essentially defunct and so I therefore now Linking video:uploader to a profile on the domain such as http://www.yourdomain.com/blog/author/bill-alderson/ which I imagine will be correct if you're using WP and Yoast's plugin. However, I wouldn't expect adding the uploader element to return anything specifically for you at the moment, given the way rich snippets currently stand.</video:uploader>
I have updated the blog post to match this advice.
Having rel=author to each page on your site wont affect the way Google read your sitemap, but it may mean that Google elect to show the non-preferential Rich snippet for your page, dependent on the search results. I have seen instances where this has happened on an ecommerce platform with a plethora of schema markup and Google then return authored results for product pages, rather than the ideal star rich snippets.
As long as you have the Page locaton Thumbnail, Title, Description, Content_loc (for .mpg, .mov, .mwv, .mp4 files) or Player_loc for .swf files then Google should have all the info they need to provide rich snippets. Anything above this is ultimately a luxury and if you're relying on automated tools to create the sitemap as you have a large bank of video content - then in honesty, I probably wouldn't worry too much about it.
I am yet to find a decent video sitemap generation tool, so am actually currently in the process of building one. The Wistia sitemap generator you mentioned should do the job just fine for you in the meanwhile.
Cheers,
Phil