Hello,

the link in the SEO dashboard for the HTML sitemap is only for testing purpouse, and has not the Joomla menu alias assigned.
To have a link like this http://www.domain.com/gegenereerde-sitemap/sitemap/html with the alias to menu use the standard Joomla menu creating a new item for the HTML sitemap.

second question, if you mean exclude the menu link that point to the HTML sitemap from the sitemap itself, just use the menu item exclusion feature. Opening the menu data source in edit mode you will find the control to exclude single menu items from the sitemap.

Greetings

John