Is it possible to make the units going to the black hole go slower to it? I am referring to the black hole obstacles in bounds where you get sucked into the middle and then blown up. How would you do this? Make burrowed units underneath? Are there different speeds possible?

Yeah, you'd have to use burrowed units constantly moving under them to slow them down, if you want them to get pulled in at a slower rate, you can just use a death count to make it so rather than ordering them into the black hole every trigger loop, you only do it every other or so.

The more frequently you run the "order" action, the stronger the pull of the obstacle will be. With hyper triggers, full-speed ordering makes a pull too strong to fight against successfully; as you space out the orders, the pull gets weaker and weaker, easier to fight against by clicking constantly. If you want an example of different gravity strengths, see here. You can also slow them down using burrowed units or by periodically stopping them with a method of your choice.