This particular use of 'less' with a countable noun doesn't offend me personally, but I'm surprised that such a large corporation as BMW isn't more conservative in its language use. (My, ahem, Reader's Digest Oxford Complete Wordfinder describes 'less + countable noun' as "disputed".)
Google gives 64,000 hits for "less emissions" and 93,000 for "fewer emissions" - far closer than I would have expected. I suppose it might be because, although 'emission' is a countable noun, we rarely talk about 'one emission' or indeed any specific number of emissions.
AskOxford on less vs fewer