Hey Dave,
Yep, you can use wyUpdate to silently check for updates when your app starts. Then, if updates are found, you can quickly close your app and launch wyUpdate to finish the installation. We have a full C++ example on the "How to Silently Check for Updates" article.
Secondly, what are some alternatives to WyBuild on the mac?
I've heard good things about Sparkle. It's not as easy to use as wyBuild, but people like it.
Tell me if this helps.