If you are relatively certain that Vista will install to a single partition you select using Recovery, then go ahead because as long as Win7 is not wiped out, you can add it into the MBR using EasyBCD 2.0 from Vista.
Vista may also configure the Dual Boot as it should.
Win7 is fully recoverable either way, even if you have to recover it's MBR to add Vista back from there.
http://www.sevenforums.com/tutorials/5166-dual-boot-installation-windows-7-vista.html
Personally, I would find a clean-copy Vista installer to unlock and clean reinstall Vista without the bloatware albatross.