just checked again :
that riff is played as intro by a guitar (clean/crunch) and/or a bass
less driven than in the cover, more laid-back style. the saturated guitar is the lead one
just before the chorus (sort of a "bridge") the vocals sing "back on the dance floor" on that same line : first Mark alone, and then background vocals
an then, background vocals sing along this line : "doowap doowap"...yes I am serious
and then again the pre-chorus and the chorus
the outro is "doowap doowap" by vocals with synth lines, and lead guitar licks
and the end of the song is just "doowap doowap" by vocals.....yes I am still serious
so yes that line is the main theme throughout the song, a little bit faster than in the cover video