As a personal viewpoint, if vectored off the STAR, I wouldn't expect the SLP to be complied with if it is a waypoint. (Let's not get in to the possiblities of factoring in RNP performance and what is deemed to be 'on route' within the centreline, whether vectored or not
)
But I would expect compliance if the SLP is a DME distance (which is therefore not dependent on you being exactly on the centreline).
Regardless of that view being correct or not, the '250Kts 3 minutes before the holding facility' is a good catch all which I believe embraces the 'spirit' of the procedures and allows for any interpretation by pilots being vectored by providing a speed reduction requirement several minutes before reaching the holding airspace.