Do you have any pictures? How bad is it? My first breeder male, Sid, had a slightly dipped head. Nothing too serious and he made 1st place in his class at a show so it obviously wasn't seen as a fault.
Some people think any form of a dip is bad. Personally I want to see no dip at all but paired with a female with a good topline I think it should be easy to correct.
Pictures would really help. Depending on how drastic it is is going to determine if he should be bred.
Photo's will help a lot to answer this question....A LOT of top winning Betta fish have dips behind the eyes...And most of the imports I have brought in do....I think newbies are confusing this look with some of the deformities that the DT's produce...