The tritium sights are both. The purpose of the tritium gas in the vials is the beta particle radiation it emits that strike a phosphor coating inside the glass vials and make it glow. Having a source of light fueled by a radioactive source is called radioluminescence. Beta radiation can only penetrate about a quarter inch air and can't penetrate skin, so is fairly safe as long as you don't inhale the tritium gas. Tritium has a half life of about a dozen years.
It was unsafe gamma radiation from radium that caused it to be a health hazard. Too bad. It takes about 25 years just to lose just 1% of its energy, IIRC.
As for the recommended paint additive, they claim you can see it for 24 hours, but don't say how dim it is by then. Whether or not it would be bright enough to use by the end of the night, I don't know. It's a common practice to hit watch dials with a flashlight to get them glowing. Might need to do the same with it on sights.