I was asked this question and also explain why it is detrimental to the android system as a whole.
I have not found a web page which refers to this specific question about Dalvik and swap space. Any links would be appreciated or an explanation.
What I have answered is
Swap space is a method of using secondary storage of the device to free up RAM. This would not work on android as it is not guaranteed that a device would have secondary storage causing the application to crash.
It is also slow to read from external storage as Dalvik is a JIT compiler this may lead to the code being compiled at a rate which is effecting the users experience with the app.
An initial decision of Dalvik was not to support swap space. Explain what swap space is and why it would be detrimental to the Android system as a whole.