i think its good, consider that they have a good portfolio in writing, a worth prices for the articles....
There is no harm in trying a freelance writer from India or Philipines ,etc , Just ask him to write a small article first before you give him/her bigger project.
I always recommend that people hire writers that speak the same language of the hiring party. If you don't, you may deal with some serious syntax issues not only in the final product -- but also in the contract you're working with. And I just know you are working with a contract, right?
each person is different I would say generally they would have poor writing skills that are not natural english but sometimes you can find some good ones. I say its better to do the writing yourself and get manual article submissions and tedious work outsourced cause you NEED GOOD ARTICLES AND WRITING SKILLS