Is it a safety issue to only bring the hot wire onto a board for mains switching?
Does not bringing the grounding wires onto my board present a safety
  issue? I feel like it won't, but I haven't worked with mains before
  and am a little hesitant to say it with certainty.


It does present a safety hazard, from arcing between the wires and/or traces on the board. If you're using this in a product with regulatory testing, then it needs to conform to IEC 61010-1 which specifies the minimum distances to avoid arcing between traces. Wires also have a clearance of their own.


Source: http://www.pcbtechguide.com/2009/02/creepage-vs-clearance.html

If your board does not need to go through regulatory testing it's a good idea to design it with the clearances in mind anyway because it's safer.

If you have a question on the pollution degree, its related to the type of environment the board will be in: 



Source: http://www.ni.com/white-paper/2871/en/