Will KLH interfere with GST or HIS tag in antibody generation?
Carrier proteins (such as KLH) are used when the antigen is too small to be antigenic by itself. Peptides smaller than MW 6,000 are usually conjugated to carrier protein, while peptides larger than MW 6,000 are considered large enough to be immunogenic without a carrier protein.
If GST tag is used, no KLH should be necessary, as GST is large enough. If HIS tag is used, then it will depend upon how large the tagged protein is. If a synthetic peptide is used, typically 15-20 residues, then a cysteine can be added to either end during synthesis to enable conjugation chemistry through the terminal cysteine (this assumes there are no internal cysteines).
Probably best to use GST and not have to worry about conjugation to a carrier protein.