I'm not seeing where there would be a blank line (blank line should not be confused with empty, or null, field). Can you post a screen shot of the merge template?
I think I know what the OP wants to do - that is, where no logo is applicable, then all the logos shift to the left... or right... or remain centered.
I've tackled this before and have an answer... even have a tutorial for it on my blog. Go to http://colecandoo.wordpress.com/2012/02/19/going-beyond-stencil-letters/ and then go to 4: SCRABBLE LETTERS and have a read of that. There is a PDF to download which has attachments inside of the indesign file and assets used to make the tutorial.
The key to getting the images to disappear is fourfold.
First, the image frames have to be inline graphics one next to the other, aligned with whichever text feature is appropriate.
Second, the picture placement options in the merge have to be "fit frame to content"
Third, there can't be "blank" records in the csv/txt file when there is no picture. instead, create a "blank.pdf", or download the one i've graciously decided to host on my site: http://colecandoo.files.wordpress.com/2012/08/blank.pdf
Fourth, the PDFs going into the fields must be using the artbox to get it's measurements. I find that this can be accomplished by placing a PDF image with "show placement options" turned on, then selecting the artbox for the measurement, then clicking ok. until it is told not to, any PDF placed in any file from that point will use that artbox as a reference until it is told not to in the "show placement options".
Again, my blog has a tutorial and sample to play with. Good luck.