Scaling

If you Scale uniformly (same amount on all three Axes), there shouldn’t be a problem with Texturing here (as UV’s are being used as Texture Coordinates), but I’d recommend Applying the Scale anyway.

I wouldn’t use a Lattice to simply Scale an Object (although it’s possible), but if you use it to distort a Mesh, weird things may happen to your Texture, the noticeability depends on (the regularity of) your Texture:

Different Texture Coordinates give different distortions, but often you can get away with it (especially with hand-painted Textures) if the Lattice deformations aren’t too extreme.

If you Apply the Scale, you should be good to go. If you don’t Apply it, unexpected behavior should be expected.