Ultimately they all just output a 0-5v signal.

So as long as whoever is mapping it is happy with seeing different numbers, then the map sensor you use is irrelevant as long as it covers the range of pressures you need.

And as said before, looking at the scaling for the Weber 3bar sensor, it's pretty close to a GM 3bar sensor anyway

So again, after checking the mapping, really no reason why they couldnt be used. Although to be fair, most of them seem to come from China now too.
I see a place on ebay.com.au selling a GM style 4 bar map sensor for not bad money

http://www.ebay.co.uk/itm/4-BAR-MAP-...item1e9ab9832a

But there are better quality local options...more expensive too

http://www.jti.uk.com/product/map-sensors/

VW use a 4 bar map sensor on a few of their cars...pretty sure some of them aso have an integrated temp sensor too.

edit, DTA lists part number as 0281 002 316 for the 400kpa sensor
0281 002 456 for the 350kpa sensor