He cannot send the passport to New Delhi. The only way to send the passport to NDVO is through VFS (in India or Nepal). VFS will accept the passport only in person. Either your husband has to submit his passport by himself or authorize someone else (by a letter) to submit on his behalf. When the passport comes back, again either your husband or someone else who is authorized, has to collect in person from the VFS office. VFS office also has an option to mail the passport back to an Indian address. This is generally how it works when the applicant is in India or in Nepal.
I am not very sure how it works if the applicant is not in India or Canada but some other country. Does your husband already has PPR and does it say to submit at VFS in India or Nepal? You can also try calling VFS in Qatar to check if they can send it to NDVO or VFS in India. Or if your husband already has PPR, try writing an email to NDVO and check if he has an option to get the visa stamped at Abu Dhabi VO. In worst case, your husband should be prepared to travel to India.
