"part" of Austin.
There are two qualifiers for Hays County. Because it it has great economic interchange with Austin, has 50% of their population living in urban areas, etc.......
Even if it qualified to be an "outlying" county with SA, it would not be included in the SA-NB MSA because it can only be included in one and if it qualifies as a central county with Austin, it cannot qualify as an outlying county with SA.
http://www.census.gov/population/metro/about/
As for Kerrville joining the SA-NB MSA; we discussed it in an older thread talking about the new census numbers. I think we all agreed that if it ever qualified for the 15% interchange or some other new standard, that it would be included which could happen the next round of census.