When you pronounce '서울하고' as '[서우라고], it is called 'free allophone', which means that the pronunciation depends on the speaker. Phonologically, you have to pronounce /ㅎ/, but in modern Korean /ㅎ/ weakens as /ㅇ/. As for your friend's pronunciation, it is wrong phonologically. It is acceptable practically though, which means that many people pronounce and understand it. * When you pronounce '좋아', you have to pronounce it as [조아], not [조하]. It is not 'free allophone'.

But some other Korean told me that I can read this sentence "도쿄는 서우라고 비스테요." and I even checked it on the internet and I found "서울하고" in a different sentence and this person (who is Korean) also pronounced it "서우라고".

Ebbie is right

Nopee, you must pronounce the ㅎ here as well^^