They should be fine but if it's a male the male from the pair will probably fight with him and you'll get some ripped fins. If the long finned is a female get another female german blue and a male. That way you will have a nice family with no aggression. The male will breed wtih the long finned.
It's not a long finned green ram, just a long finned blue ram. One of the man made ones, like balloon.