In theory, absolutely.
But let's examine this closely. There is a presumed life time for any silicone seam and at the end it will fail and the tank will leak. Adding additional stress on the seam may be expected to cause the seam to fail earlier than it would have if there was no stress upon it. The amount of additional stress upon a seam from wavemakers, or a bad stand that holds the tank unevenly, or from carelessly banging into the seam(s) during algae scraping are just a few of the stressors that might shorten the life expectancy of a seam.
A properly constructed tank seam should last many years. How much additional stress that hanging an overflow and pipes off the back of a properly assembled tank might be negligible, but clearly using heavier schedule 80 pipes would increase the stress load vs lighter schedule 40 piping.
How can we know the seal lifetime until it fails? So many variables are hard to resolve and I submit that a properly assembled tank can be expected to fail with or without a drilled overflow putting additional stress on a tank, but thus far no one has determined if that extra stress is killing seams and causing failures at an increased rate. I wouldn't worry about it as much as a bulkhead seal failure since I read about those often and have dealt with them fairly frequently, and often those seal failures are from over tightening the bulkhead that was designed to seal by hand tightening them.
In conclusion, I don't really know but I think it's a possibility but not a significant one unless the overflow is improperly installed.
