Yes you do.. you have no choice... Nik does that as part of the process.
I'm sorry.. it doesn't. When you select "edit in" and select "Silver Effex", then select "Edit a copy with Lightroom adjustments", as soon as you do this, it creates a second copy as a TIFF, and then that point on, whatever you do in Nik, you're working with that copy.
What is it you feel Nik has that LR doesn't?.. apart from the cheesy presets that is.
When you view an image generated by Lightroom on screen, just what do you think you are seeing?
It's not a raw image, because a raw file is not an image file, and if you sent raw image data to your graphics driver card it would have no idea how to interpret the data.
It's a bitmapped image generated within Lightroom, that you are seeing, and all the adjustments created in Lightroom are applied to the bitmap, not the raw file, which is why the raw file remains untouched.
Once you move the image outside Lightroom it
has to become a bitmap, but provided you maintain adequate bit depth, then there's no penalty in carrying out further edits.
I must confess that I'm not a fan of B&W processing, I don't do it very often, and the only reason I have Silver Efex and Topaz is because they each came as part of another package.
You've already disqualified yourself from judging either program by saying you don't have them, so it's not up to me to justify their existence.
All I can say is, when I have played with them they seem to be capable programs and I rather liked the results I could achieve with basic programming, although less so with their "film simulation" modes.
I joined this thread in order to contribute something that might be helpful to the OP, not to start a debate on the methods and merits of different pieces of software.