This is debatable, since the original (and most common) definition of a "wyvern" is just "a two-footed dragon", which implies wyverns are a dragon subtype.
Fantasy often distinguishes between two-footed wyverns and four-footed dragons, but not consistently, so there's plenty of wiggle room for different fictional settings to use different fictional terms. According to RWBY's official concept art, this is a dragon: https://rwby.wikia.com/wiki/File:Grimm_Dragon_Concept_Art.png