Does a sulfuric acid/nitric acid mixture dissolve PTFE (ie. teflon)?
I can't claim to have any personal experience with that sulfuric acid/nitric acid cleaning mixture specifically, but, as far as I'm aware, PTFE is generally inert towards acids. As a testament to that, it is apparently the material used for storing fluoroantimonic acid. I found a chemical resistance chart confirming its stability against strong acids. It is evidently resistant to concentrated sulfuric and nitric acids, as well as aqua regia (a concentrated mixture of nitric acid and hydrochloric acid). I have used the last of those for cleaning PTFE lab equipment before with no problems.

Having said all that, it would be wise to consult the handling and safety data for your particular labware to be certain.