Without root, no. Rooted, with the proper frameworks and calls in the boot image, possibly. It is hard to accompluish such things without converting the entire build. Some items get by with the standard build, an extra framework here or there, and permissions to allow said frameworks in the boot. Most require the framework-res of that build, also. That is where you tend to run into issues and start needing a frankenstein build.
Some of the 2.1 HTC widgets can be used with a Stock 2.1 Droid (look for the ones without a matching odex file).. but they are not really worth the effort.
I forgot which ones I tried now, they were that unimpressive.