Rational Test Workbench is not dependent on Worklight. There are 2 RTW Mobile test options -
1) Rational Test Workbench Mobile Test Edition, and
2) Rational Test Workbench Eclipse Client
Either of which can test worklight applications. The difference is related not to Worklight, but to how the tool will be used in a scaled environment.
There is a version of RTW Mobile Test Edition that is included with and can be installed with Worklight called IBM Mobile Test Workbench for Worklight that can only be used to test Worklight apps. (See the subheading "Testing with IBM Worklight in the Worklight online documentation.)
RTW Mobile Test Edition is a stand-alone mobile testing tool that can test mobile applications using either a simulated mobile device or a real mobile device. (See http://www-01.ibm.com/support/knowledgecenter/SS2HS7_8.6.0/com.ibm.rational.test.lt.rtwm.reldoc.doc/topics/rtwm_readme.html)
RTW Eclipse Client is a component of the Rational Test Workbench, and is the same thing as the RTW Mobile Test Edition, however, it can also be integrated with the features of other Rational Testing tools including Rational Integration Tester and Rational Quality Manager. (See http://www-01.ibm.com/support/knowledgecenter/SSBLQQ_8.6.0/com.ibm.rational.test.lt.rtw.reldoc.doc/topics/rtw_readme.html)