Is it correct that the regulations do not prohibit the mixing of ETBE RFG and MTBE RFG at any point in the distribution system?

Yes, provided the segregation restrictions in section 80.78 are met. (7/1/94)

This question and answer was posted at List of Reformulated Gasoline and Anti-Dumping Questions and Answers: July 1, 1994 through November 10, 1997 (pdf) (2.98 MB, July 2003)