I understand that Aprimo is supplying customer service driven products. I suggest to do a exercise before start using ETL tool for the mighration, whether Pega 7 platform is enough for the migration or Pega Customer Service or any vertical application needed or not.
Coming to ETL tool, It is up to you which one you would choose. As per the information I have, Pega does not recommend any specific third party tools when migration is specific to cross plotform. However, Pega has its own tools when the migration is form lower version of the Pega to Higher version.
By the way, I did not worked on the exact stack(Aprimo to Pega) you have mentioned. However, I worked on other BPM to Pega (BPEL to flows) .