I use DLM, and I don't have to add a ramp or anything--it never gets more than a few inches deep, because the ducks compact it with their feet, and the soil organisms are constantly breaking it down from below anyway. Of course, it may be different if your winter is colder than ours, because it may not break down as fast. Also, wood chips won't break down as fast as straw does. Anyway, my ducks are capable of getting up a pretty steep incline from the lake without trouble, so I think it would have to be pretty steep to prevent their access.
I do use straw without trouble, but again, it may be different if you have a less mild climate. And yes, the ducks do bury their eggs. But only if they are starting to build a nest and want to keep the eggs, in which case the nesting area is pretty obvious and it's easy enough to dig around and find the eggs. Most of the time, they lay right on top of the bedding in some place completely illogical, like next to the gate to come out so they have to walk over it on their way out in the morning, or next to the pool so everyone steps on it and poops on it while hanging around the pool.
The ducks don't scratch, and I don't mix. I start with just enough bedding to cover the wire that lines the bottom of their pen, just to keep it from hurting their feet. Each morning, I add a very thin scattering of straw, just enough to barely cover the poop (but I can usually still see the bedding below the thin scattering). This keeps the flies down and prevents the ducks from walking around constantly in muck. I lay the straw a little more heavily in the areas that are especially messy.
I only change the bedding completely once a year, and usually by that time it's around 6-8 inches deep.
Under the straw, I have a thin layer of wood chip mulch that I use to cover the wire. It is usually completely composted by the time I change the bedding, along with much of the lower half of the straw bedding. I toss it all in a large pile to finish composting, and then use it on the garden beds in the fall. I spread some of the bedding directly around the base of the fruit trees, without letting it finish composting, and it acts as a combination fertilizer/mulch. My trees do very well with it.
Good luck!
