a PPI is never a bad idea. I'd trust the word of an experienced BMW specialist whose time I was paying for to do a thorough, meticulous job...over dealer techs going through an assembly line of cars and probably being rushed by the sales department. also, I'm surprised at how cursory these "200+" checklists seem to be, even for CPO. I haven't seen the BMW one, but the Porsche and VW ones were kind of eye-opening for me.
the dealer does have every right to refuse, but I think you'd be wise to walk away if they insist.