Yeah, for that you'll be fine, but take Rhino for example - Rhino offers, through LiveConnect, the ability to create JavaScript objects, at runtime, that satisfy Java interfaces. Which is cool, and useful for a lot of stuff. But the version of Rhino you can use on Dalvik has all of the bytecode generation disabled (obviously) and as a consequence, it can't emit the necessary bytecode to create the interface-fulfilling Java wrapper to make the JS object do what you want. It's generally bogus.

Also it's really hard to express how much slower Dalvik is than HotSpot in the general case, too. It seems faster with the Android 4.2 version (by about 30%, in my highly unofficial testing) but it's still pretty agonizingly slow.