[watchfirst9]

Yup even in non-cantonese city like Shanghai or Beijing those variety show they will sometimes sing Cantonese song or speak in Cantonese but never heard them sing Hakka or teochew song.

mC while promoting Mandarin use but did not limit dialect use especially in music
Many workers from other provinces working in GuangDong. 
HK singers of older generation able to sign Cantonese and Mandarin along with  
its TV dramas from 70s 80s 90s were board cast in mC are leaving lasting impact in entrainment sphere. 
 
New trend is songs contains Mandarin mix with other dialects. 
Cantonese is most common, there are still few others as well but rare
https://www.youtube.com/watch?v=C-LgHh7x27I