the opposite.  if the AO is in the material, you don't need it to be in the lights and vice versa.  IDL does it's own version of occlusion, so you don't want to use material AO with IDL either.  you don't want to use light AO with IDL, for that matter.  you always want your occlusion to get calculated in only one way.  so use IDL or light AO or shader AO, but not any of those together.

edited to add: not that it will damage anything to use two forms of AO  together, it's just unnecessary and a little less accurate.  sort of like applying a shadow twice.