Chaos Spawn wrote:None are slowed ever because they get Move Through Cover as a unit special rule off the Independent Character, who gains it through being cavalry.
Cavalry "are not slowed down by difficult terrain (even when charging)" but only have the Fleet and Hammer of Wrath special rules, not Move Through Cover.
I would say that as cavalry the Wolf Guard Battle Leader is not slowed, however he is joined to a unit of guardsmen which per the
IC rules he counts as part of for all rules purposes, and it is that unit which is making the charge. So if when joined to that unit he or any other member charges through difficulty terrain the unit is slowed per
RAW.
HIWPI perhaps would be that if he alone charged through difficult terrain the unit would not be slowed, though if any guardsmen did so he would be slowed with the unit.