Either way is valid. If you float it, you won't get a nice transition from the bolt to the base that it's on but if that doesn't matter ... sure, save the triangles.
There's a couple of scripts in this thread: http://www.polycount.com/forum/showthread.php?t=71406 (and more floating around PC, giving the search function a healthy workout might be an idea)
It depends what you mean by use really. In a game the best you can hope for is BC5 on current gen, which is a high quality 8bit format. I would always recommend baking to 16bit (float or integer) when authoring textures. :)
Ultimately you are truncating floating point normal data into 8 bit per channel color, ending up with integers stored in less than 24 bits per pixel (as not every color is a possible normal). Another issue is that interpolated values between pixels in the normal map will not always match what you think the absolute correct…