it is in eurosystem isnt it?
If you mean in eurozone (countries paying with euro) then yes.
Then you are allegedly safe up to 100K per account... for now...
EDIT:This may apply only for Euros though, not sure about foreign currency
But the real question should be is your account at Bitstamp, even when is fiat, whetehr USD or Euro, considered a "bank account" and under the same protections as someone with say a checking account at that same Slovenia Bank? I don't know the exact answer but my guess would be no. You do not technically have a bank account at the Slovenian Bank. Bitstamp does. Bitstamp holds money in your name under their account, most likely commingled with other peoples funds.