Yes, using PhotoLab, sending an image to the Nik Collection creates an intermediate TIFF file, which the Nik application writes its edits to. This TIFF file can continue to be edited in PhotoLab without altering it, because PhotoLab, unlike Nik, is a non-destructive editor. It uses sidecar files to store adjustments and some metadata. (Other data is kept in a database.)
Your other question about Nik vs. PL + FP + VP has been addressed before in other topics. Most recently, here: