I struggle with this one, for when I was first into the construction industry as the "new guy" the "young guy", other senior guys would say "hey, young buck, here's a task for you". Get the "young Buck" to do these tasks.
I had to look up on the internet and do a couple of key word searches. I changed the wording, how I looked, and in 5 of my keyword searches, First Nations and "young bucks" never came up in my searches, and I did move off the first page.
Example here:
https://ca.search.yahoo.com/yhs/search?publisherid=58020&type=BIZM_3010510014_$58020_000000$&hspart=Lkry&hsimp=yhs-SF3&obt9bpdyed=0&p=what+does+term+%22young+buck%22+refer+to¶m1=mT_VyuK_N8qBpBSxAlcLA92-b_ISBNPauWrQIEJfQwLIc8nylcPcTstlJJj15g7O5yQbv2U60i8O8reGiVrC2sWw80dekKNYRVHQmKbYrV3TFo-QyqcE0DEB8xqRKR2Ilizh2UHGx26gmy3eRSHvOg-M8HKQXDOf4f2pgsfKDPeStNrxr1B-hyTFhO3p3D6K667vhnooB0qe2_ahIGSHlciQR9s1lirFNezeE5th1hTnyyNB7M4_iNdAN6Lg3N23-wk%2c
If anything, young buck came up most often as slang for a young male. In some of the sources, some references were made towards African Americans, and Ronald Regan and his use is alluded to.
My conclusion is that many cultures and nationalities seem to have used the term "young buck" as it has developed and evolved. I am not sure if I would categorize it as derogatory and targeted towards First Nations people. If anything, the origins may have originated with African Americans, and seems to be a term often used in those circles.
In my research, I even discovered that if you talk to the right people, the term "uppity" can even be considered derogatory depending who you talk to.
Dano