Can't see why not.
Zebra loaches should be kept in groups of 5 or more. Keep on a fine sandy substrate in order to protect the delicate sensory barbel area, and ensure that there are plenty of hiding places in the aquarium amongst bogwood, caves, and plants.
Guppys i've always been led to believe best kept in 6's, and like some plants and hideaways, someone will correct me if i'm wrong.
Mark