Absolutely. But you'll need some way to get participants to see your ethnio screener - if you have a site that's live, or are planning on taking out Facebook ads, LinkedIn ads, or even tweeting out the link to your ethnio screener - you need to drive traffic to your ethnio screener on your own. We don't provide any panel of people. You might want to check out usertesting.com for that.
Assuming you have an existing site or method of driving people to your ethnio screener, once you have contacted them, you can simply run your research sessions however you like. Ethnio is a tool for simply finding the most accurate participants possible for research - what kind of research you conduct and if you have them use a prototype or mockup, or simply discuss concepts with them, is totally up to you.