Having a reputable bounty manager is somehow needed but not necessary since this could increase the confidence of bounty participants to join on your campaigns. There's a lot of scam campaigns which can possibly affect your program if this is not been handle well by experience person. But its not mandatory but if you think your team is good enough and can handle the job then its fine you can run a campaign on your own but make sure you have an escrow to secure the funds of participants so that the community can tell that you are serious with the campaign you are running willing to pay everyone who made efforts on your marketing campaign.
I just noticed that you are saying that a reputable bounty manager is not necessary and not mandatory. Tell me, do you have a hidden hate with some of the reputable managers? Or maybe you are hiding something from us here? Hhmm. It come to your own mouth that a reputable bounty manager can attract participants but isn't that a good thing for the project? This means they will be promoted properly.
Another thing which can help attract participants in a campaign is when the participants see that the funds are escrowed but there are some participants who will check first if the escrowed tokens are listed on a good exchange or it has a good volume or not.