Honestly depends on EWR traffic conditions at the time. I've had situations where I fly into EWR and land ahead of schedule, other times we're circling for half an hour waiting. If I were you, I'd look to see what's the next departing flight to LAS from EWR. Having flown with Continental EWR to LAS, there are quite a few as I remember. You may want to see if they (Continental) would be willing to change your flight.

So, after all that, I'd say: Can you make the connection in 30 minutes? Iffy.