Maybe the problem is in considering that "channeling Unlife" is magic in the first place.
As far as I'm concerned, it is not. Evil spell lists are not "of the Unlife", they are still of the Essaence (and of a deeply corrupted will, at that). A Essence caster that learns Evil Magician spells is still within the Essence realm. I've always thought that tagging those lists "Evil" was basically slapping judeo-christian morality on top of an agnostic magic system, even though Shadow World does not necessarily follows judeo-christian morals in what is "good" and what is "evil". Perhaps "Tainted" would have been a better tag - tainted use of the Essaence, which would imply that the Essaence is an energy that can power almost any effect but that has a "domain" - a polarity, if you will - where some effects 'go with the flow' while others 'go against the flow'. Or perhaps the untainted uses of Essaence are linked to the Lords of Orhan, while the tainted uses of Essaence are linked to the Gods of Charon - after all, the Essaence shares a common origin with those entities, and the polarity of the Essaence is mirrored in the polarity of the quasi-divine entities. In any case, Unlife is another thing entirely.
I even think that non-spell users should not be at a major disadvantage over spell users to handle Unlife "energy". After all, the Hunger consumes everyone equally. It is not possible to be a "hybrid" in that Unlife and Essaence cannot coexist in a living body. "channeling Unlife" means trying to control something that is antithetic to one's own existence - until the Unlife finds purchase in you, takes hold, and starts consuming you from the inside, keeping the shell but replacing the energy principles with something that can naturally channel Unlife, but not Essaence anymore.
In technical terms, I would
- not consider Unlife capabilities as spell lists, but as distinct powers, at least until the Unlife has taken over the channeler's insides.
- those powers are neither subtle nor easy to control. It's not manipulation, rather unchecked release. Until one is consumed by the Unlife, there is very little in the Unlife except sheer annihilating power.
- the more one channels, the more powerful the effect and the higher the chance that the Unlife finds purchase and "nests" in the body.
- once Unlife has found purchase in a channeler's body, Unlife powers become controllable (spell lists and variety of effects). However, the Essaence powers become uncontrollable (no more magic - channeling the Essaence becomes as difficult as channeling the Unlife was before the change, with the same degree of subtlety and control. Basically, you can only release raw energy of creation and change, and nothing structured). this goes until the Unlife fully consumes the insides of the channeler, at which point the poor thing cannot channel Essaence anymore and the transformation is complete.