It's possible to graft fairly distant plant relatives to one another (cherry and pear to an apple tree, etc.). Cross pollination, however, is quite difficult between different species of the same genus. Most non-tabacum tobacco species will not effectively pollinate N. tabacum. One of the underlying problems is that the chromosome number often doesn't match between the two, and even when it does, the information (genes) on specific chromosomes are frequently scrambled in a different pattern. N. tabacum pollen is apparently capable of crossing to a Nicotiana rustica blossom. So unbagged rustica may produce some hinky seed.
Tomato x tobacco cross-pollination seems improbable.
Bob