I am happily using inskcape 0.48 on 64 bit Windows 7.

-Using

/Extensions/Generate from Path/Extrude...
/Extensions/Render/...

I can do some 3d Object creation inside blender.

-Is it possible to rotate these 3D objects inside Blender?

-How do I do this?

Is there some SVG viewer program out there, particularly an open source one, that I can use to do this?

Happy new Year!

-Is it possible to rotate these 3D objects inside Blender?

Inkscape or Blender?
In Inkscape, it can only rotated in the 2 dimensional plane. Use Selection tool, click twice on the object, grab one of the corner arrows and drag. Or you could use Object menu > Transform > Rotate tab. You'd have to use Blender to rotate in the 3rd dimension (2nd plane).

I'm not familiar with SVG viewers. Inkscape has a native viewer -- look for Inkview.exe. But all it does is display. If it has any controls for zooming or rotating, e.g., I haven't found them. Actually, now that I think about it, I don't think there is an SVG viewer for Windows.* But of course Inkscape itself can rotate, as I mentioned. Depending on your needs and purposes, you could use Inkscape, and hide all the toolbars. Not sure if that would work for you?

* There used to be a plug-in for Windows, known as Renesis Player. But the author/creator literally disappeared almost 2 years ago. I actually have the last (most current version) and could send you the file. But it doesn't work on ALL SVG images. In my experience, it displays almost half of the SVG images that I come across. I'm not sure if it can rotate. I'll have to find an SVG image that it can display, and look closely at the context menu. I know it can zoom, but I can't remember about rotating. If it can rotate though, it would only rotate in the 2 dimensional plane. PM me your email address if you want the file, and I'd be glad to send it

No, that was a typo: I only have Inkscape 0.48 in mind.

Is it at all possible to rotate inkscape 3D style objects, as described in my initial post,
through all 3 dimensions?

Sorry, no.

Are there any third part (free/open source) programs that support 3D rotation
of these inkscape 3D objects?

It's my understanding the Blender can, although I haven't personally used it.

Are there any free/open source programs that can rotate these inkscape "3D" objects,
particularly in an svg file? Could someone there make a good recommendation?

svg specification is in 2D. any 3D effect is faked, just like in painting or drawing. this is very unlike the 3D simulated environment in blender, which supports natively movement in three dimensions. so while it's probably quite possible to import svg file into blender or such, the object will only be flat. this might be good enough as say a texture, mapped onto a flat object, that is always only seen from front.
i have seen someone's programs that do manipulate svg back and forth to create live 3D looking simple environment...but that is all custom code, and nothing like the ease of manipulating objects in programs like blender or povray.
for simple (or as complex as you dedicate time to) declarative objects, i think you can't beat povray.
then again..all 3D in computer graphics is an illusion...so as long as you're not looking for a very speedy shortcut..there's always a way.