My sauerkraut has mold covering the surface, is it ok?
Per NC State's Extension's article on pickles and sauerkraut (some emphasis added):


  Pickles or sauerkraut mold during fermentation. 
  
  Answer:
  
  Unsafe—microorganisms are growing  improperly.
  
  Possible reasons
  
  
  Fermentation temperature was above 75&deg;F. 
  Too much salt was used,
  not allowing adequate lactic acid production. 
  The cloth on top of
  the kraut was not kept clean during fermentation (may need to be
  replaced after skimming).
  


Per Penn State Extension's Saurkraut Guide (emphasis added):


  Do not taste it if you see mold on the surface, feel a slimy texture, or smell a bad odor.


Their PDF on Saurkraut says:


  To avoid surface mold  growth, keep the cabbage submerged at  all
  times by covering it with a plate just  small enough to ft inside the
  fermentation container or with two or three clean  quart jars filled
  with water. An acceptable alternative is to fill a large, sealed, 
  food-grade plastic bag containing 4½ tablespoons of  salt and 3
  quarts of  water.


Again, no indication of acceptable types of mold.

I cannot endorse the existing answers which indicate that mold  is an acceptable part of the saurkraut making process, unless credible science based evidence is presented, from reputable sources such as University Extension Centers or, better yet, peer reviewed journal sources.