I’m a little unclear as to whether you personally are (1) supplying/“arranging” a consignment of pistachios to an ice cream manufacturer (2) are the ice-cream processor yourself, (3) are buying/brokering the ice-cream finished product ?
If (1) the micro issue is usually controlled via an agreed (micro) specification between buyer/seller, in respect to both processing method and final micro. numbers. In practice, afaik, the primary reason for pre-treatment of such raw materials by, for example, heat is usually twofold ie (a) to eliminate zero-tolerance pathogens like salmonella which are frequently associated with such items, especially where the intended use is as a direct ingredient of a RTE product and (b) to lower the values of total plate count and coliform which are interpreted as having hygienic significance.
The previous post covers many of the possible options in this case.
If (2/3) the specification aspect IMEX is usually between processor and retail customer and particularly with respect to the safety of the RTE finished product. IMEX the spec. usually includes both processing and micro. details. Not my product area but offhand I would anticipate that ingredients like nuts in ice-cream would have strict control requirements, ie pre-treatment probably mandatory. Numerically the usual route is for R&D to make trial samples for testing/agreement purposes by processor/buyer.
As I mentioned, the micro. limits you initially quoted are afaik for ice-cream, not pistachios. If the coliform values you mentioned earlier refer to already heat - treated pistachios, then there may be a problem with either (1), (2) or (3).
Perhaps you could clarify the situation.