Life's to short to take shortcuts that only cause momentary savings...
You will probably have problems, maybe not immediately but sometime in the future it will probably come around to bite you. Mixing high and low level is a great way to test your troubleshoot prowess in the future, just hope everything is grounded correctly. I never trust air to be a shield, at least put something metallic in between them, especially if there is any safety concerns/ risk.
Heck, you can have problem running 480VAC wires from one device runnning next 480VAC to another isolated device. We just blew out a VFD last week because of a 500mcm 3 phase/ 3 wire feed to a 50 hz generator in our Lab shared conduit with an air compressor (#3 3 phase/ 3 wire) for about a 60' run. A 30 to 40 year old air compressor was replaced with a new energy efficient one earlier this year. Good grounding wasn't required for the old compressor but that new VFD sure wanted to have a good ground (which we though we had). It was seeing over 700 volts to ground which the some of the silicon had an issue and it let some smoke out.