It could be different, yes. But it could be exactly the same too.
We don't know what the disc for Promo OST looks like, so it might be the same as the one we see included with Limited Edition.
This would make things easier for them to do just one pressing and use it for a couple of purposes.
Also the catalog number looks different from the OST by Sumthing Else.
MHTMCZEN14
It's that "ZEN" part that seems to appear in European (promo) releases.
For example:
ZENCD 100P
ZEN CD100
Hitman Contracts Limited Edition (Xbox) was released in Europe (maybe only in UK) so that's another step to make a connection between the two.