This is true. What the person did was ascribe a GM-Fiat only power to standard Ally Spirits.
No, there are defined spirits types which have this power, just none of them belong to any tradition I'm aware of. They all tend to be shadow spirits, ie sucubus, and the like.
It is possible to find one, then banish/bind it, use it to drain karma, then use a spirit with endowment to endow the sucubus with endowment, and have it give you karma drain to get the karma from it, but I'm not sure how well that would work out. The sucubus would have to never be allowed to accumulate enough karma by itself to upgrade itself, because if it did, it would kill you in ways so terrible the english language doesn't yet have the vocabulary to describe. You would really have to come up with something 'interesting' to placate it, so it doesn't goon you.