Can undesirable karmic entanglements result from any exchange of bodily fluids that might contain cellular DNA, such as saliva, semen, and fecal transplants?

This can indeed happen. In most cases, the magnitude of the carryover will be minuscule and not long-lived and will be broken down within the body of the recipient and excreted. So the effects will tend to be more minor and short-lived compared to large volumes of material transfused or transplanted. While fecal transplants can involve large volumes of donor material, it has relatively few cells from the donor compared to the microbial content, so it consists of a very small amount of nuclear debris largely from the turnover of the epithelial lining of the gut. Much of that gets metabolized within the gut lumen prior to excretion, so anything transferring to a recipient in the course of a transplant will be relatively minor in impact.