As others have mentioned, there is no cook book answer. If you are diving from shore, then the size of the waves is critical. If you are diving from rocks or boulders, it may be easy to jump in and very difficult to get out in the same location.
If you are diving from a boat, then a lot depends on the boat and also the configuration of the ladder and/or platform. Even the gear you are taking matters, if you have a small or moderate sized tank you can do a lot more than if wearing a heavy exposure suit and multiple tanks. Also, realize that water temperature matters a lot too, if you get really cold, you will experience significant weakness in the arms and legs and this affects your ability to scramble up a ladder on a pitching boat.
If you have a long period swell, (this is large waves that are gentle and spaced out far apart because the wind energy that generated them has dissipated or the waves have moved away fro the generation source) it may be easy to dive in a 10 ft swell. However, larger swells can penetrate deep (100 ft even) and move sediments around and can make it dangerous to dive next to a shipwreck that will concentrate the surging water.
Of course, a huge consideration is the strength of the diver. There is no substitute for physical strength and endurance. Also a huge factor is the experience level of the diver, have they dove in similar conditions, do they understand how to climb a ladder or scramble over rocks? Realize too that if you get in trouble in the "white water" which has zero visibility, your buddy can do little or nothing to help you.
Determining what conditions are suitable and which are not is probably the hardest aspect of diving and it may take years of practice and maybe even several close calls before you get a feel for what is doable and what is not for you (and any buddies who have so little going on in their lives that they have to dive in marginal conditions).
Can't write this much without a "one summer in band camp" story. I was diving near a shipwreck in 100 ft of water with 10 plus foot swells. The surging action was not too strong, but the ship was creaking and groaning like a haunted house. I went under the stern of a 300 ft ship to shoot a fish. I shot the fish and got totally slammed by a surge so strong that it snapped the end of my gun off when the shaft didn't fully exit my gun and the surge threw me forward further under the ship. It was a real lesson in the power of surge and how a ship could funnel the wave energy in a small restricted place.
