If I understand your scenario correct, you want to have moderation to the comments of the blog post you have in Sitecore. I will just give your different solution here.
The template you created for comments can have one more field "Show On Website", so when the user submits the comment, this field will be unchecked. Once your author validates the comment and is okay to display on Frontend then s/he can check this field. In your MVC view you will have a logic to check this field value to display the comments.
If the above logic is implemented, then you dont need the additional db (ugc).
Second scenario to see the data of Master DB and comments together, you can create a new publishing target with Target Database as "master". And create a scheduler to pass the comments from Web DB to Master DB in specific intervals.
So when the Authors login to Sitecore Interface, they will be able to see the Master content and the user generated comments in one place.
Hope this helps. In case I have confused you, we always connect to discuss it further.