As far as I'm aware, the only real fight between the Hulk and Gladiator took place in Incredible Hulk Annual 1997, but I wouldn't necessarily call it definitive for two main reasons.
Firstly, the version of the Hulk featured in that issue wasn't a standard version. During the conclusion of the Onslaught storyline in the mid '90s, Bruce Banner and the Hulk were physically separated, and Banner was transported to an alternate, pocket universe created by Franklin Richards, along with various other characters, such as the Fantastic Four, the Avengers and Dr. Doom.
The Bannerless Hulk that was left behind had unusually low durability, making him more vulnerable to penetration wounds than most Hulks.
Conversely though, he was stronger than normal, since he was channelling energy from the same pocket universe Banner was trapped in.
This situation came to an end when Banner and the Hulk were reunited in Heroes Reborn: The Return #4, but in the intervening period, the version of the Hulk operating within the Marvel 616 universe was decidedly non-standard.
The second reason I don't consider that Hulk/Gladiator fight definitive is that the Hulk exploited Gladiator's vulnerability to a certain type of radiation by shoving him into a nuclear reactor. It was at this point that the fight became a one-sided beatdown.
In addition, the fight was quite poorly written in general. For example, the Hulk managed to deduce that Gladiator was vulnerable to a certain type of radiation, based on the fact that he was hurt by having his heat-vision deflected back into his eyes, which is quite a logical leap.
Moreover, Gladiator had previously flown through a red giant star in Marvel Comics Presents Vol 1 #49, and it was stated that he was "oblivious to the raging nuclear inferno". You'd think that a guy who could handle flying through a star shouldn't have much trouble with a nuclear reactor.
Gladiator also mentioned that he'd flown through stars in the same issue where his radiation weakness was first established -- Fantastic Four Vol 1 #250 -- which suggests the type of radiation he was vulnerable to was supposed to be very specific, and not something likely to be found within a random nuclear reactor. (NB: That's not actually Storm zapping Gladiator there, but a Skrull imposter using Skrull tech. Same goes for the other 'X-Men' present in that scene.)
Finally, the fight began near the aforementioned nuclear reactor, but after they flew to the edge of the atmosphere and went through reentry on the way back down to Earth, the odds of them landing next to that same reactor -- which they did -- seem pretty astronomical. Even if they travelled up and down in a perfectly vertical line, the rotation of the Earth beneath them should've caused them to land miles from where they started. Suffice it to say, Lady Luck must've been smiling on the Hulk that day.
