Are Doctor of Arts (D.A.) degrees in math taken seriously?
If the NSF (National Science Foundation) doesn't recognize a degree as a Research Doctorate, for whatever reason, the holder's opportunities will be limited. For example, most colleges and universities in the US expect faculty to do at least some research at some level. The required quality varies widely. 

Tenure in the US is determined by faculty committees. If one or more members of your committee doesn't accept the quality of your degree for whatever reason you will fare poorly in attaining tenure. 

Finally, when you apply for grants you are expected to list your "highest" degree. If a "doctorate" isn't recognized as a Research Degree by NSF, you might need to list an MS as your highest degree. This can be devastating if you don't expect it. 

For the D.A. degree, NSF recognition as a Research Doctorate ended in 2003. 

Note that the above is directed to anyone who would want to pursue this degree now or in the future. Consider the above issues. However, it says nothing about the quality of the people holding the degree. Many were unfairly left stranded, unfortunately, by NSFs change of designation.