You can promote your own posts yes, the only thing there is that if you upvote the poshtoken comment and your own share is included you won't get any Hive rewards, it's just to prevent people from selfvoting their own shares constantly which could be considered as selfvoting comments. Instead part of them go towards @hive.fund and the rest to other people who shared them.
One tip is once someone shares your post on Twitter, you can vote the comment up, it then may encourage others to also share it as they know they'll get part of those hive rewards depending on how the tweet performs. This for instance gives holding HP another small advantage as you can use it to incentivize people to promote your content on web2 and get it more views.