Probably.
More like, there would be another thing that converts various elements into whatever they need (da f- is plasma product anyway). That will use the power the fusion reactor produces to do its thing.
After all, it's just a fusion reactor. Apart from funky stuff with neutrons, it only turns hydrogen into helium.
Culture noob salesman: That clearly worked! We should make all our technological trade pitches this way!
Culture Mind: *facepalm*
Hello, the Necrons have antimatter confinement. Me thinks they outgrew fusion sometime back in the last couple of million years.