As for a personal link, I wouldn't be surprised if the two bands knew each other in the 70s. For sure they were on the same bill at a huge June 1975 concert at Wembley:
https://www.youtube.com/watch?v=KldSglCoYaU
There was a lot of interplay between the Beach Boys and Chicago and their producer Jim Guercio, who were also very friendly with the Eagles & their manager. Carl and Dennis Wilson, as well as Al Jardine, sing back-up on Chicago's "Wishing You Were Here." Guercio owned Caribou Ranch, where Joe Walsh and the Beach Boys recorded. The Eagles also stayed there on at least one occasion when they were touring in the area, IIRC.