In the contrary of vanilla trapdoors, carpenter's hatchs don't let player pass if he use ladders on a hole in the ceilling, with a open hatch.

This is by design. The only door that players can climb up is the hidden hatch when it opens downward. I may eventually revisit this idea for the remaining hatch door styles.

So actual trapdoors are completely useless. We're forced to use ugly vanilla ones instead.

You can glitch around the issue if you have full-bounding-box ladder-interaction turned on in Forge. You climb right up to the hatch, and pop it open and closed and open while still climbing up.

That's... interesting. What's the intent behind that decision?

They originally weren't intended for ladder functionality. I can add it, it's just that most of the designs are 3/16 thick, which sticks out farther than ladders. The hidden door is only 1/8th, so it wouldn't collide in the same way. Granted, I can give them no collision when being used as ladders -- that's no challenge.

I will look into adding the support for this soon.

I never had an issue with this. Even the vanilla hatches won't let you climb up if you put the hinge side of the trapdoor on the same side as the ladder. The solution is to leave a one block space vertically between the hatch and the ladder and put the hinge side opposite the side the ladder is on.