now my questions is
why are they banning bounty hunters for promoting such project??
You must know the forum rules before promoting such and it's pinned on this section:
Unofficial list of (official) Bitcointalk.org rules, guidelines, FAQ.how did they think bounty hunters or bounty managers knows about the project if it's scam or not??
If they have gathered enough information and proof of how a project being a scam. They don't accuse a project without validating and providing their proofs.
does bounty hunters or participants of such project requires to be ban or suspended??
This is also your question number 1.
I m afraid of promoting project now because I don't know the particular project that I will promote that they won't block my account or ban me
You can set a basis base on the standards of good bounty managers and what projects they manage.