Can a TransPort in IP Passthrough mode connect to Digi Remote Manager?

Yes, enabling IP Pass-through mode should not inherently interfere with connectivity to the Digi Device Cloud / Digi Remote Manager.

Related KB articles:

HOW TO: Configure IP Pass-through mode on Digi TransPorts
HOW TO: Add a Digi TransPort to your Remote Manager account
Firewall concerns for outbound EDP connections to Device Cloud or Remote Manager