No, the SPEC boot retains the grease inside the ambient chamber. Being flexible it also transmits ambient pressure to the grease and in turn to the piston. The trim boot, like the one found on your MK15, is mainly dressing but may also provide a bit of protection against impact. The trim boot has nothing to do with transmitting ambient pressure or holding grease in the ambient chamber.
The ambient chamber can be packed with grease whether a SPEC boot is installed or not. However the grease is not as protected from loss as it is with a boot.
Pretty much correct-but the original SPEC boots do the same as the DIY boots. I think what might be the source of confusion is perhaps you've seen a picture of a MK10 trim boot that also fit over the ambient ports. The MK10 trim boot had holes in it and was there for aesthetics.
Grease (silicone or PTFE) does enter and exit the ambient chamber (in very small amounts) to allow for piston movement. That is one purpose of the boot-to prevent loss of grease.
