LOL... You really made me laugh! That's like the best question ever on YA! I'm starring you and adding you in my contacts.
Although the aqeedah of Tableeghi Jamaat is not very strong, they are still Muslim (although Maturidhi), unlike some other sects. Their problems, apart from maturidhi qaeedah, are use of weak ahadeeth, as you've mentioned, then belief in "mubarak" number of days for 'khurooj', the 'khurooj' itself (the asHab r.a. did go out to da'wah, but not the way Tableeghis do it), not practicing forbidding of evil, lack of knowledge on fundamentals of 'aqeedah, not preaching aqeedah...
You're right, Arabs are extremely rare in Tableegh, although there are some, and I have met some Tableeghis from Syria in Makkah when I was out with my friend. They were trying to preach their stuff to us, but at the end we nded up teaching them about tawheed...LOL
Nice guys though, very eager for Islam, they've listened to us alhamdulillah, and distanced themselves from Tableegh, and used their stay in Holy Land to learn more about true Islam.
Some of the Jamaat-e Tableegh are on shirk though, and are thus no longer Muslims. Extreme Tableeghis are rarely found among Arabs, but common in South and South-East Asia.
Give your father some great works of Ahl al-sunnah wal-jam3ah to read, especially Ibn Taymiyyah and Ibn Qayyim, and show him this site, it contains data about Tableeghis too (in my sources).