I've seen a number of good players that could not buzz or at least not well. I've also seen lip buzzers that were lacking in other skills and were not good players. Some of this has to do with the players perception of what they are doing. Total playing comes about when every trumpet related act is done in the same manner. This includes lip buzz, mouthpiece buzz, low c , high c , 2 octaves over high c, long tones, stacatto notes everything played with the same embouchure. One problem here is that few people look at themselves playing so it is very easy to end up taking minor short cuts. At the Stevens Embouchure Clinic every student was taped so that they could see the changes that they were making.
Most people will buzz easier in a smile embouchure so they try to adopt it. This false buzzing does not help. It really needs to be the same embouchure that you actually play. Most players who have limited themselves because of embouchure end up with 4 and sometimes 5 different types of embouchures that they use.
They have a
1) lip buzzing embouchure,
2) a pedal tone embouchure ( meaning they can NOT play pedals with the normal setting ),
3) the real embouchure ( low c - g on top of the staff ),
4) a shifted setting when several high notes are played in a row ( they will take a breath here and reset the chops )
and finally some even have an
5) I'm tired setting that they play.
It is easy to start this type of thing and is also very deceiving as these changes are used to help in times of stress. You are not watching yourself and you are working your rump off to play NOT constantly checking to see if you are playing only one setting. I was at a HS band function Monday night. The band gets 1's at all contests. There were 3 trumpet soloists and all 3 used multiple embouchures. BTW that band has 2 directors both trumpet players with masters degrees.
I've outlined ways to change this before if you missed it some are on my webpage, others are on Ole and Runes pages.
Some free lessons and info about my book.