Arial of course knew this, a man as prideful as Harald would surely not bow his head to his rival but he might accept the aid under the guise of saving his family.
Harald is different than Alderam. And as such, the way to handle them both had to be changed.
But Harald also knows that he could not openly support Arial.
After all, Harald influence lay in him being the embodiment of the national feeling; for him to appear as the supporter of Arial, an Arrandian would have been to lose the crown for himself.
And homage itself is no degradation, even in the highest; a man often did homage to any one from whom he had received any great benefit, and Harald had received a very great benefit from Arial.
Harald family is now safe, their position restored even though weaker, at least they got to keep their heads.
Homage to a new lord does not imply treason to the old one.