They are not allowed on the Performance level.
Xanthan gum and guar gum are allowed on Lifestyle and KickStart
The definitive list of prohibited ingredients for Performance and Lifestyle is as follows:
Xanthan Gum (Allowed on Lifestyle)
Guar Gum (allowed on LIfestyle)
Nitrates & Nitrites
Benzoates (includes: BHA, BHT, TBHQ)
The Kick Start Level does not prohibit these ingredients.
You can view (and download) all the food lists and the level comparison chart here.