「動詞の連用形に助詞「て(で)」が付いた形に付いて、その動作者が話し手または話題の人物のために何らかの動作をすることを表す。 」
「他者が話し手または話題の人物に、その利益となることをする意を表す。」, "
What I get from that is this:
(auxiliary verbs)
Attached to the verb's continuative form following the particle te (or de), expressing the action of the doer doing something for the purpose of the speaker/person indicated by topic.
Expresses the feeling of the other party doing something towards benefiting the speaker/person indicated by topic.
I've always known くれる as sort-of a less formal way of saying くださる, indicating something being "brought down" and done as a request for the speaker, not the other way around (isn't contempt in giving expressed with ~てやる?). In the case of Issunboushi, the Daijin is overjoyed, so wouldn't it make sense for him to ask Issunboushi to marry the princess? Given the use of honorifics and the general flow of the story here, it just doesn't make sense to me that Issunboushi would be the one saying that.
Just my thoughts. You've much more experience than I so I'm looking forward to your response. Pretty amusing that such a complicated issue should arise out of such a simple story.