I have used a Rift for a short period but not in DCS. Used to use a Vive 1.0 as my main HMD and moved to Vive Pro about 6 months ago both used a considerable amount with DCS. Vive 1.0 is broadly same as the Rift (apart from weight, fit etc) in terms of specification and performance.
For me this comes down to a few factors...
Cost vs performance: Vive Pro price is significant, is it worth the extra cash over the Rift?...that depends on how happy you are to split with the cash and how badly you want a marginal improvement in resolution over the Rift. There are problems with the Rift that you wont completely escape in the Vive Pro such as the God Rays from the bloody horrible Fresnel lenses. The Vive Pro still has SDE but it is reduced in comparison. The extra resolution is a great improvement but its not night and day, you get used to it and there is still some way to go. I can read all gauges with a mild PD increase e.g 1.2. and its good enough to do ACM effectively but longer range target spotting is still not easy.
Will you be using room scale games? Its generally accepted that the Vive/Vive Pro has the best tracking solution on the market so if you want to have a good room scale experience this should be a factor...for me it was.
You'll need a 1080ti or better to capitalise on the higher resolution of the Vive Pro (in DCS), if you don't have the horsepower you wont get the benefits.
Given that the PiMax 5K+ has just launched which offers further improvements in resolution and much bigger FOV (for around the same cost) I would be seriously look at that option too. Its not perfect (see the reviews) but could be the sensible choice at this stage. Odyseey+ is also available and might pip the Vive Pro as the resolution/FOV is the same, but its much cheaper. However I'm hearing the comfort level and general build quality is not great and the tracking is not as good either (unless you use the Vive sensors).
Hope this helps