Probably. Although the cog and lockring will probably be installed on the hub, they will not be tight enough to prevent the lockring from loosening as soon as you ride the bike and the cog tightens up. As the cog tightens, it pulls away from the lockring, causing it to become loose. Then as you back pedal or skid, the cog unscrews until it contacts the lockring, and eventually through several cycles of forward and backward pedalling you will end up stripping out the hub threads and will need to replace it. So, IMO, a lockring tool is essential from the git go, although you don't necessarily need a chain whip to tighten the cog.