chestnut is agouti, and dominant over the otter gene. Self is recessive to the otter gene.
It depends on the breed and what is "recognized" if you care about showing your animal.
A homozygous agouti AA, will only ever give you more agouti [chestnut] animals, no matter what you breed it to.
If your chestnut is either Aat, or Aa, you will get a variety from crossing with atat or ata.
I breed agouti and otter to each other all the time, since i like a variety of colors.
I'd be more concerned about breeding an otter to a tort, aa ee, since there are no breeds that recognize torted otters.