The important thing to note here is that no colubrids (sensu pre-Pyron 2013 ) possess venom glands, but rather have adapted their Duvernoy’s gland specifically for the production of toxins. So the question is really this: do we call something venomous if the venom is being secreted from a gland that is not a venom gland sensu stricto, but has instead converged to serve a very similar function?
The dentition of Heterodon is strongly opishtoglyphous (as the name, which means ‘different teeth’, would suggest):
This dentition indicates to me that there is some injection mechanism at play. As in most opisthoglyphous snakes, the rear fangs are probably grooved, which would allow venom to flow down these grooves and into a wound/prey item.
No research has been done on the secretions of the Duvernoy’s gland (a specialised gland that produces venomous toxins in colubrids) of Heterodon nasicus, although some has been done on the closely related H. platirhinos (the eastern hognose), which showed that the secretions from the Duvernoy’s gland exhibited toxic effects on in-vitro muscle and injected mice . This would suggest that these snakes are venomous, although only weakly so.
As for the effect on humans, I found a single reliable report of human envenomation by H. nasicus , which showed that these snakes can have medically significant bites, and given the evidence from H. platirhinos discussed above, it is reasonable to infer that this toxicity is likely produced by the Duvernoy’s gland and not the salivary glands of these snakes. This also addresses the question about whether or not these snakes are able to inject their venom into humans, but it should be noted that, as with most opisthoglyphous snakes, it takes a while for them to do so - the snake must be allowed to bite for an extended period in order for its rear-fangs to pierce human skin. It also shows that we may be sensitive to this venom, but I believe that this reaction was immune rather than venom-driven.
The important thing to remember is that these snakes are not dangerous to people. They rarely bite, and when they do it is unlikely to result in envenomation. Even then, the effects are not prolonged, and the patient described in ref.  above had a full recovery in five months.
- Written in consultation with hyacynthus