I'm looking into new boats and got to wondering about hp ratings. I know that a 30 hp outboard and a 30 hp mud motor are completely different in terms of weight and torque. How much of a difference does this make? For instance would a 50 hp rated transom be strong enough for a 35 hp surface drive?

Short answer, yes, it'll work.
But a dang 18 hp mudmotor will be more stress on your transom than a 50hp outboard.
Just see how much a 50hp Yamaha weighs.
These mudmotors aint light

My surface drive is probably pushing 300 lbs or so it seems at least. I just have trouble with being comfortable with the hp ratings. I know some of the mud boat manufacturers post their hp rating with outboards as well as mud motors. But I can't imagine there would be any comparison.

there is no comparison really.
A 36 prodrive is around 330 lbs if im not mistaken.
A lot harder on the transom than an outboard.

Who gives a shit about hp ratings? You never heard of anyone complaining about having too much hp, have you?

I used to run a 16x60 custom built boat, with a 150 Johnson.
What is hp ratings?

I understand and agree with the point of horsepower. But are the motor weights factored into that as well. Or is it strictly a horsepower thing?

Up here you see more Mudmotors mounted on 1648-1848 regular Jon boats than on custom mud hulls. When we mount them on a regular Jon hull we reinforce the transom. To handle the weight, and the torque. Most are .72-.100 ga. hulls. If not abused they hold up really well. I run a modded MB BD 45 on a Alumacraft hull, which is rated for 30hp. Going into its seventh season and still pretty straight and doesn't leak. Picture is how we reinforce them.

Did you just bolt steel through the transom there denny

Looks really good. Beats paying a welder

It's funny about the HP ratings. My 1996 1856 GD has the plate for 50hp. Go to GD site and punch in 1856 duck boat, now they show 40 hp? Bottom line is if you see the transom flexing, reinforce it as the previous poster did. In the 70s I put a 6 cylinder 100hp Mercury on a 1965 17' Sea Ray. Added oak chattel knees to the transom. I go by my eyes and my gut when it comes to HP. But there is never enough! Also remember in 96 you had long tails and outboards, not surface drives.

Hp ratings are more conservative now than even a couple years ago. The general consensus is an attempt to reduce liability. If the plate is severely underrated for what the boat can handle and the user goes larger, the manufacturer is farther away from that lawsuit when something goes awry.