He's credited for sounds; his name is on the playfield, right below the "Drive Again" light. https://www.ipdb.org/showpic.pl?id=1176&picno=71282&zoom=1

(I don't know if this is because High Speed reused sound effects from previous Williams games or if he contributed new code.)

At the time of High Speed, DeMar and Jarvis were still working as VidKidz. The software for High Speed was written by them as contractors to Williams. Eugene probably helped out with some code here and there.