It will be most unlikely that the mainland police will be doing SWAT training with HK police because they are two completely different organisations although they do have some co-operation in various law enforcement activities.
It is true that all weapons in the HK police are western and their doctrine will be very similar if not the same as the British police. In addition the HK police SWAT is actually called the Special Duties Unit (SDU).
the HK flying tigers use mp5 as their bread and butter SMG. As far as I know, procurement limits on the PAP is less restrictive than PLA, I have seen pictures of PAP SpecPol with SIG 2000 and the likes.