The short answer is no. Whenever you start cutting clips, adding transitions, and filters, your going to have to render. Vegas is dependent on your computer’s processing power. The Faster your computer the shorter your render times. If you do a print to tape Vegas renders only what needs to be rendered on the timeline. Some jobs require that you render the entire timeline (MPEG for DVD as an example).
What a decklink card brings to the table is a very high quality input and output device, and high quality codecs.
Even true realtime (hardware accelerated) edit systems have their limits as to what can be played back in realtime with no rendering. For example the system I use at work will playback up to 3 video streams without rendering. Add a key over that and it’s render time across that section. Add an overlay alpha it’s render time again.
Rendering is just a fact of life unless you a doing very simple projects. We are a Final Cut Pro facility with Kona 3 cards and we still have to render.
So do yourself a favor and get the fastest computer and drives you can afford, with lots of RAM, so that render times are short.
Hope this helps.
Regards, Rick.