Dashmount GPS antenna instead of Roof-mount

If I go with a dashmount GPS antenna, instead of the roof mount one, do I still need the additional VSS (Can-BUS) steps?

On Wolfgang's website, he states that the dashmount antenna can be used as an alternative: (Wolfgang's ML Page: M-Class GPS cellphone antenna.

"GPS dash antenna
Another option is the Mercedes hideaway GPS antenna, part 203 820 0975. It comes with a HRS GT5 (f) connector which plugs right into the MCS or COMAND and 20" of cable. GPS reception on the dash under metalized windshields usually works, but may not be as optimal as with a roof antenna."

I can get a dashmount Mercedes antenna for under $100 which plugs right into the MCS unit, so I'm just confused as to whether or not this eliminates the need for the VSS source if the dash mount antenna gets this information from the satellite? Any help would be appreciated.

I'm working on the retrofit in my brothers ML first, and we already have a 2001 fiberoptic MCS installed. We also ordered the fiberoptic CD changer cable and, as long as the parts guy is right, the power connector as well. So from here, I just need to get a set of the CD nav discs and the dashmount GPS antenna (assuming I don't need the Can-BUS with this option).

Any insight would be appreciated.
Thanks