Hi
I would like to know if there is any thing in the elctrical code that talks about piping a dry type transformer instead of doing it with liquid tight flex.

Nothing.
But practically speaking piping transmits transformer noise to anything that the piping is attached to where flex dampens it.
DTDTs will product between 40-65db of noise depending upon the kva.

Victor- There are no prohibitions on using either wiring method on the primary or secondary as long as the grounding is properly installed and the rules for installing either wiring method are observed. Get's a little tricky on the secondary side if you are installing a "Grounded" conductor and where you Bond the Grounded conductor.