Breeding related snakes?

[Zephyr]

firstly they are not as likely to produce offspring being different sub species

Sub species would most definitely produce offspring, more or less capable of reproducing; I successfully ((accidentally mind you too!)) crossed Thamnophis marcianus marcianus with Thamnophis sirtalis sirtalis and all of the babies were born healthy with no deformities aside from one. As far as if they're fertile, this would be risky to test.