That is a great question!! Who's to say for sure in all of that hair! I want to say that only females have them, however, now that I think about it I guess most male mammals have some noticable spot where the nipples would be, don't they? They are more toward the sides of the body, on a chinchilla, than you might think. When I stand my girls up on their back feet and run my hand down their bellies the nipples are sort of inline with the "armpit" area. There are several on each side. Nipples are very thin nubs on non breeding females and many times very hard to find.
One way to be sure if you found a nipple is to see if you can find another one in the same place on the other side if Cheech's belly.
But, the easiest way tsex him is to take a good look at the genitals. If he is 6 months old or older there really isn't any guess work. Place your finger under what you think is his penis and gently lift up towards his head (away from his bum). If you can lift it and if you can see skin between that and his anus he is certainly a male. By this age, if Cheech is a female you will be able to see that there is no skin between the two and a slit for the vaginal opening will be present.
It can be tricky sometimes where they are younger but by 6 months one quick glance is all you need because its an obvious difference.