'Bolo' Yeung is certainly an accomplished bodybuilder (and one time occasional training partner of Lee Haney). He has done a number of MA movies since 'Enter', including Bloodsport, Double Impact and Tiger Claws 2000. He would appear to be a skilled MA despite his bulk.
In an interview conducted by Bey Logan for Impact Magazine in the early 90's, Bolo talked of sparring with Bruce many times in the filming of ETD, and also made reference to the many challenges that Bruce accepted in this time, but that they were friends and that the sparring was enough to convince him of Bruce's superiority. He claimed that most of the challenges came from the many hundreds of extra's hired for the training camp segments, many of which were aspiring MA and MA actors, hoping to make names for themselves.
The only incident reported between Bruce and another leading character from the film, was between Bruce and Bob Wall (O'Hara). Apparently, when running through the scene with the smashed bottles, Bruce was cut on the hand quite badly due to error on Mr Walls part. This clumsiness evidently angered Bruce, and upon returning to filming after treatment, lead to him not 'pulling' a kick targeted at Bob, leading to (i believe) some broken ribs.