[Plugin: WordPress MU Sitewide Tags Pages] No options to post on other sites/blogs

No, because that’s not what it is for.

It’s for *pulling* posts from other blogs to the main blog or a tags blog.

If you want to post FROM one blog to multiple other blogs, use one of these plugins instead:

https://www.ads-software.com/extend/plugins/threewp-broadcast/
https://www.ads-software.com/extend/plugins/multipost-mu/
https://www.ads-software.com/extend/plugins/threewp-broadcast/

But, if you’re *also* using SWT you’ll wind up with multiple copies of the same post in the tags blog.