No, we do not currently support tethered shooting from DSLRs within Smoovie. There are a huge variety of DSLR cameras each with their own variation of programmatic access and it simply isn't practical to support them all.
Of course you can always shoot stills with your DLSR away from your Mac and import them into Smoovie later. To do this we would recommend importing the stills into iPhoto or Aperture first and then dragging them into Smoovie. This way, images from any DSLR should work fine with Smoovie.
Smoovie supports resolutions up to HD (1920 x 1080) which will be quite a bit smaller than the megapixels coming from a DSLR so, to be as efficient as possible, Smoovie will down-sample these larger images and store them at HD internally.