Replikanto can be used with Playback NinjaTrader connection?

Unfortunately not, because Ninjatrader in Playback mode only offers 1 Sim account called Playback101, making it impossible to create Sim accounts for testing, but you can use it with the Simulated Data Feed connection, in which case you can create new Sim accounts for testing. To create multiples Sim accounts please check this post: https://ninjatrader.com/support/helpguides/nt8/NT%20HelpGuide%20English.html?multiple_simulation_accounts.htm