You also have dvbjcam there...can it be that is descrambling everything?
It is very simple: if it works with dvbviewer (what you stated), the same plugin DLLs should also work for Sky on progdvb if something gets descrambled, assuming the same oscam and oscam settings are used as with dvbviewer.
As something works, all should work, also Sky. If not, that can only mean some other plugin is decrypting and dvbapinet is not working at all.
I can't test it, progdvb crashes on my machine I don't know why.
Like this I can't help. Maybe start looking at oscam and dvbapinet logs, they might also give a clue what is going on.