Yes they can - TD used the testing host Remote Agent to communicate with 3td party testing tools. The Remote Agent uses Microsoft's DCOM protocol to be accessible directly over a network, enabling the testing tool to receive commands from the TD Client. In order for SilkTest to receive commands from TD you must install a remote agent on each host that you want to use for running tests. The TD client and testing host PC's must be on the same LAN.
The TD Open Test Architecture Guide has all the information you need to connect TD and Silktest.
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