Since the venom is rich in enzymes (proteins arranged in quaternary structure), being bitten would likely only cause localised swelling (a histamine reaction to a foreign protein in the system). There is likely no correlation between bee allergies and a sensitivity to hognose venom; however, if you have an overactive immune system then there may appear to be a relationship between the two reactions (although a bite from a human would likely elicit the same response).
It is entirely possible that the venom is harmful to humans, but it depends on the individual's physiology. Generally, it would only be a small percentage of people who would be at risk but since the venom is rich in enzymes, a person could die of anaphylactic shock. The venom is produced in very small amounts so it is unlikely to cause much harm to humans but it may be enough to subdue a toad and slow it down while being ingested.