Most cichlids(including oscars) will hide wrigglers, so not seeing the wrigglers until they become free swimming is quite common.
But pike cichlids are very efficient fry predators, and can easily and quickly swoop in grab a mouthful of wrigglers, and then just as quickly retreat.
They are also very good at picking off free swimming fry.
If you want to keep fry, the pike cichlid should be in another tank, as should any other wriggler, fry predators like Pleco's or tetras.
One of the reasons oscars and other cichlids eat their own young, is if they figure the odds are against them to be raised successfully.