In theory yes, you will have the ground typing covered. However Helioisk is a glass cannon. A glass cannon is a Pokemon such as Gengar with embarrassing defenses and an ATK/SATK capable of destroying worlds. Thing is that Helioisk is not actually that much of a hard hitter. 109 base special attack is nothing to marvel at therefore nothing more than a frail Pokemon with decent special attack and speed. Because Surf lacks stab, coming off a 109 base SATK it won't be doing as much as you would hope even to ground Pokemon. 252 SpA Life Orb Heliolisk Surf vs. 0 HP / 0 SpD Nidoqueen: 260-307 (80.9 - 95.6%)- Thats pretty much max spatk with life orb against an non invested ground type.
Surf is generally good coverage anyway for Helioisk however I wouldn't take your chances with it OHKOing Pokemon that have not already been weakened.
