I've recently these holes in the end caps of fluorescent tubes. The vintage sylvania u bent tubes have only one hole while these newer GE black light lamps have two. What is their purpose? Is it so the cement for the end caps can cure or is it to inject something into the tube to weather proof them to some degree by protecting the electrode vacuum stem wires?

I think to prevent air pressure build up (that can push off the cap and break the cement) when the lamp heats up

I would guess ventilation for air expansion (so the pressure can not build up there to detach the cement after sme time) and indeed cement curing.

I've also heard of kits that come with special silicone sealer and a syringe and you inject this into the end cap and that weatherproofs it to some degree.

I've also heard of kits that come with special silicone sealer and a syringe and you inject this into the end cap and that weatherproofs it to some degree.

There are many things sold with huge claims, but many such things just do not work as advertized, or have quite severe drawbacks.
I don't think these kits were ever approved by any of the lamp makers - in other words they do not take any responsibility, if the lamp get exposed to the humidity regardless of this treatment.

And my experience with such things is, the best humidity proofing method is to let the humidity escape as quickly as possible. The only reason for that is, the humidity just always finds the way in, regardless what you do. So you should make sure, it as well goes out as fast as possible, so it does not get enough time to case any harm. And here such filler will only make it impossible to really dry out.

Yeah I agree with you on the sealant gels not working; it will wear out fairly quick with the heat given off.