You can fly a
spinnaker using a pole without a lift but getting the sail full and gybing would be a bit messy. The lift's role obviously is to raise the pole to horizontal, however, once the
spinnaker is set and pulling with any breeze, the
spinnaker wants to raise the pole anyway...the fore and aft guys serve to keep the pole from rising above horizontal - when the
spinnaker is pulling, the lift may only matter in lulls where it keeps the pole fromtrying to droop the luff.
That said, working without a lift will be messy, plus spinnaker poles can be subject to strong loads, and are best kept under tight control, not having a lift loses one of available control
lines. I wouldn't do it on an ongoing basis.