I would say no for a couple of reasons. Guppies and neon tetra have different water requirements. Guppies will live longest and do best in hard water, and neons will live longest and be healthiest in soft water. There is a middle ground where both can survive, but neither will thrive.
A 10 gal tank is not as big as it seems. You really only have room for one school of fish. Six fish is the bare minimum that neons should be maintained in. They really do best in larger groups (go look up school of neon tetra on youtube and you'll see what I mean). In small groups like 6 and under they do have a habit of lashing out at other colorful fish such as guppies and bettas (which is why they have such a bad reputation around here). If you keep them in the size group they should be in, there won't be room for the guppies.