I think I found the problem/solution.
In the documentation Aruba Sipport sent me, a whole different format was used for option 43 compared to the documentation found publicly.
The public documentation format for option 43 is:
masterip, country-code, master-mac1, master-mac2
For me, this format is understood as:
10.100.10.195,BE,00:50:56:41:1d:16,00:50:56:41:31:74
But the confidential or internal documentation states a different format:
mip=10.9.196.160, mm1=aa:aa:aa:aa:aa:aa, cc=US
or
mip = 10.9.196.160 , cc= US, vm2= 00:0C:29:B9:20:64 , vm1= 00:0C:29:B9:20:5A, vip=10.45.34.187
So for me this looks like this:
mip=10.100.10.195,cc=BE,vm1=00:50:56:41:1d:16,vm2=00:50:56:41:31:74
And this is recognized by the remote controller :)