Crew / pacers help massively in a long ultra especially in the latter stages even if it is just for a moral boost. Potentially it can be an unfair advantage in a race were some runners are crewed and some are self sufficent.
If there are no crew / pacers than everyone is on a level playing field and its down to the individual to get to the finish line.
I was crewed on this years GUCR, but I ended up running 120Miles of it with a non crewed runner. He said the extra moral boosts he got from my crew helped him no end, he was not sure if he could of finished without that extra help...