Depends on age. Pipes vary from 1 billion to 16 million years in Arctic, just like Kimberly South Africa. (Here in this shield territory of SA, billion year old pipes such as the Premier may still be large.) If the pipe is late late, late it can be into limestone and not eroded at all. Prior to that it is up for grabs. Some pipes in Northern Ontario subcrop under paleozoic cover. Some are into Blake River volcanics. If they are Cretaceous, they have seen all the erosion since then that exposed and peneplaned the volcanics. So I would not buy that volcanic intruded pipes are less eroded.
The Somerset Island pipes were fairly large, and very widely diamondiferous (Mitchell). I don't know about crater facies but certainly diatreme. The ones that intruded the paleo in Ontario were diatreme by my core inspection. KL pipes varied but were mostly diatreme. (50% diamondiferous, and high carbonate. No good chemistry work done yet, but good looking and plentiful pyrope) Debeers said in their log that the Victor was hypabyssal, but we have not seen that. Inspection of Mountain Province tells me it was crater and diatreme. Snap lake was high level diatreme despite its limited geometry. We are seeing many crated facies pipes in the territories. Wawa pipes that I saw were diatreme texture. (Protected from erosion even in that environment by limited deep erosion of Algoman orogeny.) So I would say that it is a combination of age, and cover intruded into.
Bottom line? I would bet you could see anyhing anywhere. In the paleo, you could see deep erosion of older pipes pre paleo, and also young pipes too. But with extreme age differences, you would expect different environment, level and character. Since paleo cover areas are quiet, you could say also that late pre paleo pipes, may be not that much eroded as they formed in low basin structures.
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