is there a reason the Dilate/Erode node in the Compositor nodes has no option to be relative on the overall scene resolution? My full node setup is relative to the resolution except for this node, which is not too useful. And it even does not accept an input value. Or can the Dilate/Erode node be imitated with other, relative nodes?
You can emulate this node with others, at least to some extent depending on used mode. Talking about eroding/dilating alpha channel here, effects on color might not be that easily achevable.
Erode/dilate is based on variations of blur + clamping and scaling which you can very flexibly emulate with blur + colorramp nodes. Using different blur filters and ramps you can do most of erosions/dilations you ever need.