No, cucumbers are mostly water. Zucchini is a far superior source of electrolytes, vitamins and minerals. Huck that Cuke and ride the Zucc! Hope that helps.
Plecos do usually eat algae when they are hungry. But they also need to eat an omnivorous range of foods, light on the meaty stuff.
I can't believe so few of us have answered that for you after four days.