Can I lay pavers over a concrete patio?
If you have a drainage issue, or you're likely to have freezing conditions, I'd personally want to lay a small coating of gravel across the concrete first - allow that pent-up water to get out of the way.

If you're building this in, say, Phoenix, though, that may not really matter and laying them directly atop the concrete shouldn't be a problem.

To the 'cement' part of your question: why not go with dry-laid? As long as there is some form of rim to the patio, or you're not driving over them, dry-laying would make both maintenance and modification easier.