Joomla offers a CMS to run a website on. Joomla uses mysql databases that just hold the information that will be shown on the content pages at the front. The way it is supposed to be used you won't be able to run multiple sites on a single cms.
You can't run 2 websites with different content on that single cms, but you can create multiple front ends on one cms. You could for example store your data using joomla and get it shown at the front using your own code. This way you will be able to have two interfaces / websites on one cms, both running on the same data.
So from what I read in your question I think the answer will be NO, unless you want to just apply another presentation to your data.
My own experience: I have used Joomla to just hold news articles that my web-master will add. I just used php to get those news-articles out of the mysql database and did that to make sure i could get my own presentation for the data displayed.
