There’s the rest area at John Little Falls, too…that’s maybe 5km towards Rupert from Shames so that’s after the Terrace hills and just starting the long flat 80 km along the river. It’s only 25 - 30 km from Terrace, though.
Check out the “http://www.skeenariverrelay.com/race-information/stage-summary” page to see descriptions of the route broken down into the various legs of the relay (as described while travelling from Rupert to Terrace) with distances, hills, and pullouts listed.
Get to the opening of the Skeena and look for parts where the old highway are still together,they make for good spots to camp and there are lot’s of them all the way along.
If they are still enroute, and you are going to have further contact with them prior to arrival, I highly recommend Kasiks wilderness resort, very nice camping area, excellent restaurant, showers, a room if they want, and it is almost exactly halfway. Otherwise there are many of the other areas already mentioned here, the rest areas at George little falls ( Andesite creek ) Telegraph point, or the little creek just east of the Khyex river. Other wise as Jesus has suggested Extew is also excellentthe campsite is only 6 KM off the hwy. which may seem like a bit far on a bike, but would be very worthwhile for the scenery, and the waterfalls.