As long as the cantrips are on the Warlock spell list, the same perks that apply to leveled spells also apply to cantrips. If a cantrip or other spell is not on the Warlock's spell list (for example, if the Warlock is also a Wizard), the bonus does not apply. Warlock invocations are also not affected by the rod of the pact guard, which is an important fact. Whether it was an accident or on purpose, a Warlock spell that is cast through an invocation is not truly a Warlock spell.