The Thunder clap is a Hulk signature. IMO, DoS and HP lack the mental capacity to put 2 and 2 together to pull off a move like the thunder clap. They fight more like Bizarro, relying on retard strength and intellect, or feral Wolverine relying on uncontrolled rage, rather than Hulk that (depending on which version) fights more intelligently and is capable of using his rage to become stronger. Smarter versions like Doomslayer or GW would probably do it, but DoS and HP are pretty much just punch, kick, throw, slam. I could see HP snagging Namor like a fish, similarly to the way he did Superman.
Superman was only hurting his hand after an extended fight that had left him nearly drained and bony protrusions began appearing on Doomsday's body. IMO Namor's underwater healing ability is far superior to the Yellow Sun healing ability portrayed by Superman in DoS. If he can knock out Savage Hulk of trade punches with Sentry he can easily hold his own against even possibly beat DoS Doomsday, possibly even a Doomsday clone. Not saying he could beat all of them. Honestly, I think HP would be a stalemate, with Namor unable to seriously hurt Doomsday and Doomsday being too slow to keep up with Namor. GW and Doomslayer are a different story. Both are intelligent rather than beastial like the others. Can't see Namor beating them.
That was before he started getting drained, doomsday koed superman and martian manhunter(bloodwynd) simultaneously and turned supergirl a class 100 character into putty with one punch. He also tanked HV, martian vision, Guy's qwadrian ring's full charge, booster and Fire's attacks without even flinching. Namor isn't going to win against DOS doomsday.