You can rarely say these fish are safe with these other fish. Its really down to the temperament of the individual fish. It might work ok, it might not.
Glofish tetras are GM black skirt tetras, and these fish are considered to be fin nippers. But if they are kept in a suitable sized group they are more likely to keep their aggression within the group rather than looking to take it out on another species.
So keeping guppies in this tank with 2 tetras is more risky than keeping them with say 6 tetras. But you may have 2 very calm individuals and would be fine, whereas if you added some more tetras and then added guppies, it could be that one of the extra tetras is just a jerk and it will go for anything. No one can really say what will happen and the only way to know is to try it.
Personally i would increase the number of tetras anyway, they will be happier in a bigger group. And then if you wanted to add a few guppies go from there. But its a risk. Many people keep these fish together with no problems, if you ask around you will find people that found they didn't live well together in their particular tank.