Can I qualify for Child & Dependent Care Credit if spouse incarcerated, i.e. not full-time student, not incapable of self-care, but no earned income due to incarcerated?

You can't use the dependent care credit if you file as married filing jointly.  Incarceration is not one of the exceptions that allows you to file for the credit if you spouse does not work.

However, if you have been living separately since before July 1 (for all of the second half of the year) and you provided care in your home for your qualifying child, and you paid more than half the cost of living in that home, you can file as head of household, and you can use the credit then.  If your incarcerated spouse has income for 2018, they would have to file as married filing separately.  Since married filing separately has the highest tax rates, it's possible that your spouse's higher taxes could offset the benefit of the dependent care credit.  The only way to know for sure is to test it both ways.