No, not for breeding. Your mom also needs to consider the result of breeding a fawn to a black. If she does so, she will probably end up with pups with smutty fawn coats that have too much overlay. The only reason breeders generally cross colors is if their fawns are lacking pigment or are too light. Breeding to a black will help improve pigment where it's needed, but you always run the risk of ending up with the smutty coat which is VERY undesirable in the pug world. I would have to look again, but your Mom's pug is not lacking in pigment if I remember correctly and she's not a light fawn. Plus, black pugs are generally single coated while fawns are double coated. That is the way it is suppose to be. When you cross colors it is possible to end up with single coated fawns.
As far as the conformation of this stud goes, it's not good. His contribution in the breeding world will not improve the breed. He is too roached in his back, his shoulders are not under his body and he has horrible wall-eyes. He is also lacking in depth and fullness of wrinkle. His lips are hanging instead of full, tight and round. You are right, his ears are too long as well! I hope your Mom reconsiders what she is doing. Pugs are so overbred now that it's really sad. Take your Mom to a dog show, so she can get a feel for the breed and try to discourage her from contributing to the puppy population instead of the betterment of the breed.