I can import obj files containing a reference to an mtl file, and the textures import correctly. It should work as long as all the references are correct.

Does the obj file contain the mtllib reference?
Is the referenced mtl file in the expected location?
Are the referenced texture maps in the correct location?

"If I were a shadow, I know I wouldn't like to be half of what I should be."
Mr Otsuka, the old black tomcat in Kafka on the Shore (Haruki Murakami)