Slack on hose and venting for washer and dryer
Yes.  There are even products made for this.  Its important to have locking wheels (even if you only ever lock the front two that you can access) 
As to adding some slack for the hose, remember that this will effect drying efficiency and add additional spaces for lint/socks to accumulate which can become a safety/fire issue.  Is it possible to rig a quick disconnect for the hose?  this would also allow for annual cleaning of the hose: