I have both type contact and lead for the same email address, and they are defined as two different persons.
The type contact was created via CRM (basically a mistake) and doesn't have any activity log or information.
It seems like it's completely unconnected to the type lead (despite the same email addresses)
Is there any risk, as far as the type lead is concerned, in deleting just the type contact person? (which I don't need)
If you can confirm you don't need the contact version and it is not the same person as the lead, then go ahead and delete the contact. Create a smart list with the filter for that email address. The smart list will populate with both records and you can select only the contact to delete.