DVCPRO can only be capture natively over FIreWire connected to a third party FireWire card in your CPU. At that point you can work in native DVCPRO. When capturing over HD-SDI, the deck decompresses the stream to an uncompressed HD signal which then gets captured in the DNxHD format of your choosing.
Adrenaline will then play back SD, HD, etc, in real time when in gre/yellow mode (real timne preview) but when performing a digital cut, needs to be of all one format (SD rendered as HD, etc.) Transcoding is the process of taking one format and converting to another.
Michael