I hunt south side of Buchanan and there have been a few sightings of axis in the area based on what I have heard from others on my lease. There is a high fence place on the north side of hwy 29 about a mile west of the dam, that when the lake started dropping, they walked around the end of the fence. I personally haven't ever seen on out there though, yet. As many high fence places that are popping up around central Texas, every time there is a big rain, some will likely escape due to downed fences & blown out water gaps. That happened during that flood in '07 that almost washed Marbles Falls off the map, I was hunting in northern Burnet county on Mesquite creek. During deer season, saw something come out to a feeder before light enough to shoot, I thought it was a young Charolais calf at the feeder, when it got light enough to see, I wasn't sure what it was. After some research, determined it was a fallow. But back to your point, I frequent my lease and all around the Kingsland/Sunrise Beach Village areas but haven't seen any free roaming exotics ... yet.
"everyone that lives dies but not everyone who dies lived..."