On a practical note, I have never seen such a proposal. I suspect the reason is cost. Casework with more corners and offsets costs more to build. Also, an employee may also need the lower counter. For these reasons, I would advise against using it. For code compliance, one must create a reasonable standard for sufficient depth for accessible use. Reasonable persons will disagree on that number. Why bother?  

My interpretation of CBC 11B-904.4  would not allow such a condition as the sketch. The intent of this section of the code is to provide not only an accessible counter surface for the disabled to utilize, but also to allow a free flow interaction with an employee on the other side of the counter. By having a 42" high portion of the counter adjacent to the lowered section, a person in a wheelchair is blocked from having the same customer-employee interaction as a person with no restrictions. The entire depth of the lowered counter at 34" max height must be provided to allow for this unimpeded interaction instead of the higher employee counter condition which prevents equal access.

While the DOJ Analysis of the ADA Standards allows for a split height counter, this is not explicitly stated in either the CBC or ADA. Even though the DOJ's interpretation errs on the side of less mandated restriction, I disagree, as the intent of the CBC/ADA is to provide the greatest level of accessibility. I don't see how someone could argue that building a higher barrier on the employee side of the counter has equal or greater accessibility than a counter that has a full depth at 34" height max.

Yes, in my opinion, the service counter as designed would comply with both CBC and ADA requirements.

CBC 11B-904.4 does not contain any qualifying language that separates the differing requirements between the employee and customer sides of the counter because this information is contained in other relevant sections of the regulations.  The employee side of this counter would typically be operated and defined as an employee "workstation" under CBC 11B-106.  This would also trigger the limitations contained in CBC 11B-203.9 (General Exceptions, Employee Workstations),  This section specifies a clear distinction between what is/is not required on opposite sides of the counter.  This distinction is made in the DOJ analysis and would also apply in the CBC.  I have, on many occasions, heard "interpretations" that the code does not allow a situation to exist where a person sitting in a wheelchair may have to look upward to interact with an employee on the opposite side of the counter.   The regulations of course are silent on this issue, just as they also do not specify whether or not it is required to stand or sit on either side of the accessible counter section.

In my opinion, this design doesn't comply.

The lowered section isn't as deep as either service counter top. Providing the full 2'6'' depth at the lower counter would provide an equal sized counter but I could argue that 18'' deep would also work.

I don't see the raised employee side as a barrier unless the employee also uses a wheelchair. Most wheelchair users have to look up to communicate with almost everyone.