In campaign, the vehicles would be pretty sweet. If Halo Wars vehicles are present in Reach, they should only be in Campaign, and even then, used very sparingly because they are overpowered ones that were made to counter the overpowered Covenant vehicles that are easy to take out as a Spartan.
As for the vehicles I would like to see:
-Grizzly: Make it with a much slower cannon fire than the Scorpion, but with more power or vice versa.
-Wolverine: Maybe add a small (and weak) turret to it to help with infantry a bit.
-Hawk: Very powerful, should only be used if the lasers on the sides are toned down quite a lot.
-Locust: These would be freaking sweet to drive. Tone down the laser a bit and it would be perfect. If used like the Scorpion in Halo 3s campaign or the Walker in RF:G, it would work out good.
-Vulture: It wouldn't fit. As awesome as it would be,it shouldn't be in due to balance issues.
-Vampire: Would be interesting to see alongside some Banshees, but ultimately, it wouldn't fit.
That's my take on Halo Wars vehicles in Reach. Peace.
~Hunter
[Edited on 06.22.2009 3:46 PM PDT]