Couldn't agree with you more. The teachings of the Naqshbandi silsila - especially those of Imam Rabbani Mujaddid Alf Thani (ra) - have had a profound impact on the Deobandi maslak. I think the connection is very strong but many people don't know. Like you've mentioned that the founders of Dar al-Ulum Deoband were students of the Nashbandi sufi master and muhaddith, Shaykh 'Abd al-Ghani al-Dahlawi al-Mujadiddi al-Madani. And they weren't "just students" rather both Hujjat al-Islam Mawlana Qasim al-Nanotwi and Imam Rabbani Mawlana Rashid Ahmad Gangohi were the closest students of Shaykh 'Abd al-Ghani. In fact, Mawlana Rashid Ahmad Gangohi lived and studied at the Khanqah (yes the Naqshbandi khanqah) of Shaykh 'Abd al-Ghani in Dehli. Aside from Mawlana Nanotwi and Gangohi, another founder of Dar al-Ulum Deoband, the Naqshbandi sufi master Shah Rafi al-Din al-Deobandi (ra) was a prominent khalifah of Shaykh 'Abd al-Ghani (ra). And the first Mufti of Dar al-Ulum Deoband and the teacher of the likes of Mufti Muhammad Shafi' (the father of Mufti Rafi Usmani and Mufti Taqi Usmani), Mufti Aziz al-Rahman (ra), was a khalifah of Shah Rafi al-Din hence a Naqshbandi shaykh in his own right.