Perhaps I just have another view on the because I'm not a Wessexian and henceforth I don't have the same roleplay values. I see their offer as plausible and I respect them to have the guts to come to Wessex and offer such a thing. However, I agree on Einar's decision that a mutual truce is a good offer - and the best to be offered.
Even though I admire their guts, it still is a fact that it would be difficult to have an ally of an enemy race simply because noticing each other as allies on a battlefield or a vast sea doesn't come granted, there could be misinterpretations. :/
Also, I don't value hostilities between races if I'm given a reason to not value them, and this is a good example on how to gain small trust from someone.