Texas's ERCOT is itself not subject to FERC regs, but NERC has a "subsidiary" of sorts in Texas though, the Texas Reliability Entity; although it's a non-profit rather than a government agency (but that's also true for NERC), Texas RE does seem to have a state mandate:
The Texas Reliability Entity (Texas RE) is one of the regional electric reliability councils (Regional Entities) under North American Electric Reliability Corporation (NERC) authority. Each Regional Entity is tasked with compliance, monitoring, and enforcement on the behalf of NERC to ensure bulk power system reliability. [...]
Users, owners, and operators within ERCOT are eligible for membership in Texas RE at no cost. [...]
The Public Utility Commission of Texas (PUCT) has authorized Texas RE to serve as its Reliability Monitor for the state of Texas and for ERCOT.
Does that mean that NERC reliability standards are (in theory) enforced in Texas by Texas RE? Basically what does Texas RE do exactly, in practice?