Is it permissible to bid on tenders through a person who brings and follows them up, and is given a percentage of the profit, despite suspicion regarding the integrity of his internal relationships and his hints about the existence of people who help him in exchange for a share of his portion?

If the broker's work is limited to bringing tenders and following up on them technically and financially, then there is no harm in dealing with him. However, if he uses his money or influence to secure the tender for your company, then it is not permissible to deal with him. The indications that point to suspicion necessitate investigation and caution. If it is highly probable that his work is illegitimate, then it is not permissible to deal with him.