Hello Greg,
It seems like Salt is no longer supplying their own DNS servers when establishing an LTE connection. Instead, the network responds with Google DNS servers (8.8.8.8 8.8.4.4).
They seem to use a mix of Google Public DNS and own resolvers.
I noticed this a year ago as well: https://twitter.com/seckle_ch/status/935547795066572800
Measurements from Apnic about DNSSEC validation rate for end users of Salt and use of Google Public DNS does not show a clear trend: https://stats.labs.apnic.net/dnssec/AS15796?c=CH&g=0&w=30&x=1
Daniel