This is an interesting question. I have 2 racks and have never had any issues, but I typically don't spray my animals as the humidity tends to stay high enough just with evaporation from their water bowls.

The heat tape is on the bottom of the rack,... So I'm assuming water would drip into the tubs themselves. If it did drip onto the heattape, I think the heattape is sealed except possibly where the connectors are so it would have to hit right there to cause a problem.

If you are considering getting a rack and this is an issue for you or you HAVE a rack and are having issues from this, I would contact the maker of the rack you have or are looking at buying and ask their opinion. I got both of mine from cserpents and chris has always been good about answering questions, etc. I'm sure he could give you some tips.

There are open-sided racks available too (see the AP economy line), this would help with air flow, but might cause you to have too -low humidity readings.