I think by chain tensioner he meant chain tugs, like some track or BMX bikes use to pull the axle back before you snug the bolts up. Only works with rear-facing dropouts of certain designs.
And yeah, you can tighten the bolts down hard on a hollow axle without fear. Hollowness doesn't make the threads weaker. That may solve your problem. You might try more aggressive washers like those above, or track nuts (nuts with integral free-spinning serrated washers)