Note that depth of field markings never work precisely. The lens focuses somewhere, and it is only this exact spot (plane, really, and sometimes not even a flat plane) that is in focus. Depth of field markings show areas that will appear acceptably in focus. It's worth pointing out that everything within this range is not somehow in focus, with everything outside being out of focus – it's a gradual defocusing, so the depth of field limits are more guidelines than anything strict.

Also whether something appears acceptably in focus depends on other factors, such as degree of enlargement and viewing distance. In theory, an image made by an APS-C sensor requires a greater degree of enlargement than an image made by a full-frame sensor (all other things being equal), and so the apparent defocus effect on the APS-C image is exaggerated. So, yes, the DoF scale is for full-frame, and doesn't technically apply to APS-C. But, the key point is that the DoF scale is not a strict rule in any case, so if I were you, I'd experiment a bit and see what turns out acceptably in focus to you.