Ok, so it would be Roku --> switch --> TV input. Then I would move the dvd recorder rca cables that are in the "tv input" to the switch
Yes, one set of R/W/Y cables connects the Roku to the switch and another set of R/W/Y cables connects the DVD recorder to the switch; and a 3rd set of R/W/Y cables connects the switch to the TV (where the DVD device used to connect directly).
. . so the dvd recorder can still get a signal to record from the TV?
Not exactly - in so far as the DVD recorder does not 'get' anything from the TV itself (even under your original arrangement). DVD recorders get TV signals either from an antenna being connected to it or from your cable TV provider - in which case a heavier RG58 cable (the one with the needle sticking out) is connected to the back of the DVD recorder. This should be the case now - and needn't change.
P.S. it's possible to have a splitter on the cable installed by the cableTV provider - in this case the cable can be directly connected to both the TV and the DVD recorder (they each have a tuner). Some like it that way so that they can watch TV without the DVD recorder being on all the time. Without a splitter, all TV transmissions are coming through the DVD recorder whether you're recoding anything or not. (Either way, none of this needs to change to have the Roku and DVD recorder on a switch.)