My understanding was #1 the effects would only apply to the pet except where the pet applies an effect on the player, and #2 the results would be less predictable.
The above commentator's link indicates differently. Confirmation would be appreciated.
"Dark Servant has eccentricities that you can take advantage of when building. First off, it's not considered a pet nor a damage power, despite acting like both. You can heal and buff it like a pet, but curiously it's considered a "Special Range Debuff." So, with that in mind, something you'll want to do with Dark Servant is slot it with every damage proc you can find. Regardless of what kind of damage proc it is, it will have a chance to trigger of the Dark Servant does anything (e.g. the damage procs from the Hold enhancement sets can trigger even when the Dark Servant does a heal). This can turn Dark Servant into a potent damage power in addition to the support and control it provides."