If you want to include a reference mentioning tea tree oil as a common folk remedy but not giving directions, instructions, advice or amounts to use, go for it!  However, keep in mind that past versions of that parargraph had been edited to take out medical advice added by well-meaning editors who thought giving exact instructions on how to use tea tree oil to treat ringworm was appropriate.  That we cannot leave in because it constitutes medical advice.  Past versions of this article and other articles on pet medical issues such as ticks often wind up with edits telling people to use this household cleanser or that easily obtained chemical and more often than not, that advice is foolish and dangerous.  I probably could have softened the wording a bit but I was getting tired of editors using articles on topics such as these to insert potentially disasterous advice.  Whatever you link to, be sure it meets the reliability standard and be mindful of the potential harm to people and animals that a link to an casual recipe for a cure could cause.  I'm sure there are many decent references and quotes you could find to support the efficacy of tea tree oil as a folk remedy and the theory behind it!  As to Wikipedia's own article, one wikipedia article cannot cite another to reference a statement but... if that article already has a reference that supports the contention of it's efficacy, well, by all means nab that citation!