Does this program qualify to add the ESL endorsement to a current teaching license?

Yes, this program qualifies an individual to work as an English and ESL/EFL teacher internationally.

The certificate is not for teaching in public schools in the US. For that, you have to contact each state's department of education.

This certificate is for people who want to teach English abroad or to adults at private institutes in the US.

Besides being good overseas, it's also good for teaching at private English institutes. I've been using mine for half a year like that.