Any cucumber crop, indoor or out, will get wasp waisted cucumbers eventually. It is one reason why we grow 4-5 crops outdoors annually as this helps overcome the root death problem and may provide pollen more attractive to bees than that from older plants. Leaving your greenhouse open will not guarantee a reduction as, with so many other plants in flower, potentially with pollen more attractive to bees, may not result in enough visits from bees to result in uniform pollination. As I mentioned before, bees are more likely to seek out flowers with higher sugar content (more food for the same effort) and then, for any individual bee, it will only visit that plant specie throughout the rest of its life.