I am also using okpay for a long time and until now for alternative payment accepted since you can withdraw yoru money or exchange it into bitcoin well using their service are ok but i never tested the debit card yet but i think there is no problem using their debit card since they are active also in support..
And i think you will not experience any issue of using it because it was tested by many people from before and until now..
I found a thread here and i think it can help you to have some idea..
https://bitcointalk.org/index.php?topic=151822.0