Hey Karen,
My answer would basically be - "You probably don't want to do both, but it really depends on the kind of content you have, what you're trying to achieve and whether there's demand for it on YouTube".
The important thing to remember about YouTube is that it's a social and community platform as much as a hosting service. It really isn't the appropriate place for every kind of video content so you need to take the perspective of "Would this video be relevant for anyone stumbling across it on YouTube without prior knowledge of my brand". You'll find that people don't go to YouTube with brand focused queries very often and nor do they often click back from a video to a third party site. This means the main value you're going to get for the platform will be brand awareness (see here for more details: http://moz.com/blog/the-marketing-value-of-youtube) but in order to achieve that you need to have content the YouTube audience care about. How to videos may well fit into that category, but only if they're solving generic problems and aren't specifically focused around your specific products.
The additional problem with putting videos on both Wistia (or self hosting) and YouTube is that YouTube can end up outranking your site for branded queries, which means you can potentially drive commercially focused traffic (those who may end up actually buying something!) to YouTube rather than your site and from here it's then very difficult to drive them back to your site (click through rates from YouTube are normally less than 1%); this means that, in essence, you can be unnecessarily adding and additional step in your product conversion funnel for some organic searches.
So - in short, I probably wouldn't recommend it, but to start with you need to really work out what you're trying to achieve with your videos and determine who the audience is for this content specifically. I've written some more extensive articles about this issue in particular, so if you want more info I advise you to go have a read.
http://moz.com/blog/building-a-video-seo-strategy
http://moz.com/blog/hosting-and-embedding-for-video-seo
http://www.distilled.net/training/video-marketing-guide/
I hope that's useful!
Phil