Core shamanism is as offensive to ancient Scottish traditions, and those who work to maintain and revive them, as it is to Native American traditional people. It's not part of any of our cultures.
Look at the picture on that page. It is an imitation of an Inipi. It does not resemble the stone sweathouses found in Gaelic-speaking areas (which were more like Scandinavian saunas), and if those people do Harner shameonism, you can bet they are not praying in Gaelic or doing anything else that the Scottish ancestors would recognize. They are contributing to the cultural genocide of NDN *and* Gaelic cultures.
I have some links to discussions and debunking of the "Celtic Sweatlodge" myth in the pinned thread on Harner and Core Shamanism. This type of stuff is disgraceful.