IMG tag was not removed in wiki pages, but you can only use the IMG tag to link to external image resources. The function in vB4 to upload images for use with the IMG tag is problematic in wikis because vB4's upload system is tied to individual users, and wiki pages can be modified by many users. Also vB4's uploads don't support file history. For these reasons, you must upload images for wiki use via the FILE tag.
It looks like most BB-Codes were broken because of code we removed in Alpha 2 build 2 that we thought wasn't doing anything anymore. Apparently it was, and that it only applies on newish installations where certain BB-Code collisions don't occur (in VaultWiki 3 they did).
This is fixed on your install and in the next release. Note that HTML isn't working because you have HTML disabled for the area your article is posted in. Your permissions only apply if HTML is enabled in that area globally. Also, your permissions only apply to wiki comments, not to pages. Since other users can edit wiki pages, everyone would need the same BB-Code/HTML permissions anyway or the HTML would keep breaking every time it gets saved.