A picture of the output would help in diagnosing the problem.
If the graphics are fuzzy, it is likely because they are being inserted as raster graphics (e.g., if the graphics are being inserted as PNG or JPG images). Even if the graphics are EPS or PDF they still may be raster, however that is a function of the program that created them in the first place. I would suggest trying to export the graphics from UML Diagrammer in the form of an EPS file (if you are using
latex) or a PDF (if you are using
pdflatex). If that still produces fuzzy output, then this may be a limitation of UML Diagrammer.
For more information, I suggest you read the answers to How do I insert an image in LaTex so it looks good on print?.