Hi jim78b,
Let me clear up somethings, pdf files can be either raster or vector. If you import the file into Scribus as vector, then the artwork is now part of the Scribus file. If you place the pdf file into an image frame, I believe it is considered a raster image, but I could be wrong on that and then it will be considered a linked file. A linked file stays connected to the original image/file when modified those changes will be reflected. An embedded image no longer has a direct connection to the original file, at least as far as I know so no updates would occur, you would have to replace each embedded image.
If you import the logo as vector, you can modify it within Scribus and then copy and paste it as you need it. If you would like to update the artwork across multiple instances then linking would be the best option to do so.
Cheers!
mnawij