Yes. Most people coming from lower elevations can feel the effects of altitude sickness upon arriving in Denver. It is a good idea to stay hydrated and take it slow on the booze. It hits you a bit harder up here!
Denver is lucky in that we get to enjoy 300+ days of sunshine. That being said, we also have a motto that goes, if you dont like the weather, wait 5 minutes. The wedding is at the end of June. It will be a hot, dry day (fingers crossed) but where the wedding is at, a storm can come rolling through rather quickly. Dont worry though, in the event we have a likely afternoon thunder storm, the venue will be moved inside.