We are installing a dishwasher into an old house that has never had one, and want to know if it would be acceptable to drill a hole in the cabinet floor underneath the sink to run the hose through? We originally drilled the hole in the side wall of the cabinet, with the hose coming up the back of the DW, but the hose is blocking our ability to push DW all the way back. We thought if we ran the hose underneath the DW and up through the under-sink cabinet floor we could alleviate this problem. Are there any potential water/mold-related pitfalls in placing the hole in the 'floor' as opposed to the sidewall?
There is nothing wrong with this and whether the holes are in the side, back or bottom of a cabinet is entirely related to where the utilities are located and the ease of bringing them in. If you end up with lots of water under your sink, it will find its way below regardless of if there is a hole for a pipe.
If you check your dishwashers installation manual they will usually recommend utility (water, drain and electrical) placements for ease of installation and servicing.
Mine was run through the "floor" of the cabinet. I haven't had any problems with it.