I'd be interested to know where you heard this? True tempered glass will "Explode" into little tiny pieces if you attempt to drill it. There are many tanks out there that are drilled first and tempered later (this is how they make RR tanks and some custom tanks as well).
Well you already know how to check your tank to see of it's tempered so I'd say that's step one. There are lots of HOB overflows in operation that don't fail, Lifereef from what I have read is your best bet, Eshopps is a close second and they both use the exact same design.
Are they a pain to tune and keep quiet, absolutely, but there are ways around that as well with a little research. You already outlined all the ways needed to ensure that your system will never overflow, the biggest one being keep the return chamber as small as possible. It's the Water volume being pumped back up that causes the issues and if you can limit that you're okay. As mentioned above you can also buy a DC pump like the Reef Octopus Varios line that comes with a float switch that can turn your return pump off in the event the siphon does fail.