Are the kanji in 世話【せわ】 as in 世話になります used for their meaning, or are they ateji? If they aren't ateji, what exactly is the reasoning?
Not being of Chinese origin does not necessarily imply being ateji (in the sense of only borrowing a kanji's sound with no or hardly any respect to its meaning). 文化、文明、民族、思想 are (according to the Japanese wikipedia) 和製漢語 as well, but do they qualify as ateji? Also 大根 (広辞苑). Conversely, there are words of Chinese origin where each character is used for its sounds only, eg many imported religious terms.
According to gogen-allguide and 広辞苑, 世話 originally signified exactly what the kanjis suggest: "common talk", 日常語, 口語. It then acquired the additional sense of 日常的なもの, an object of daily life; and 面倒をみる (look after/take care of sb.) during the Edo period.
As for the shift to its current sense, there are various hypotheses: (a) It derives from 忙【せわ】しい, which would make the spelling 世話 ateji; or (b) it is an extension of the original meaning, 「人の為に言葉を差し挟む意から」(広辞苑) (words spoken in the interests of a particular person).