Even if we assume Dooku knew it was all a set-up so he could face Anakin and Obi-wan in combat, he would be operating on the presumption that he was going to win. What did he think would happen from there? It’s not like he could just drop Palpatine back on Coruscant at that point. There must have been some other plan that was both worthy of being Palpatine’s plan B in case Anakin failed the test and able to convince Dooku that it was plan A. To me that has to be something more than just immediately allowing the Republic to track him down and rescue him, which could easily raise unwanted suspicions.