In an S Corp or C Corp, they are considered as shareholders by the IRS, not partners. Thus, the K-1 provides dividend information, not partner earnings, and none of that is counted as compensation for retirement plan purposes.
In an LLC, the determination is made based on how the LLC has elected to be taxed. If they elect to be taxed as a corporation, then see above. Otherwise, if a partnership or sole prop, then yes, the K-1 is used, with adjustments, to get your net earnings from self-employments which can be used for reitrement plan purposes.
edit: typo