有難う御座います is one Kanji spelling. However, I thought, 'is ございます here an auxilliary verb, and thus are the Kanji incorrect?' Should the proper spelling be 有難うございます?
Jisho says you can use both forms:
Even though I suppose Japanese only use the kanji on formal texts. The kana-way is probably better for a daily-basis use, as mentioned here.
1What do you mean by "Jisho says you can use both forms"? (1) I don't think the WWWJDIC (the database used by jisho.org) makes any style recommendations and (2) it even says "Usually written using kana alone".– Earthliŋ ♦Aug 24, 2015 at 17:43
@Earthliŋ Not exactly a style recommendation, but they desire to have the most frequently used form as the 'surface form' (i.e. first of the listed variants.)– oalsAug 24, 2015 at 18:42
ありがとうございます is a greeting which was lexicalized long ago, and I don't think it's a good idea to analyze it like this and try to apply the modern style guideline.
And while most of the recent style guidelines do say hiragana should be used for auxiliary verbs, this is not a strict rule. Not many people strictly follow this in daily life. I can't say, for example, 起きて下さい or 見て貰う are incorrect.
At any rate, the most common form of this greeting is ありがとうございます, in all-hiragana. 有難うございます is usually acceptable, but it looks a bit too stilted by today's standards, and a strict person may stop you from using this in a business email.