I can't really think of specific issues you may encounter with what you're doing currently because I never went down that road when I was learning to code HTML and CSS. Because I learned there are tags already for ordered and unordered lists on this page - HTML Lists - that's what I would suggest investigating.
I can think of some potential pitfalls. So read on and bear with me.
In early versions of RoboHelp HTML, the development team had to do a bit of finagling in order to coax the bulleted and numbered lists to appear somewhat "normal". So they styled this using the tagging that you have observed.
I'm unsure exactly which version of RoboHelp HTML introduced it, perhaps version 8? I'm just not certain. But at one point things changed and we have what we see today.
In the world of HTML, a list is tagged behind the scenes in the HTML code as either <OL> if it's a numbered list, or <UL> if it's a bulleted list. If you create an entirely new project, the CSS that is created is basically an empty shell. It's up to you, the author, to "flesh it out" and configure the styling to suit your own situation. So you have to open that CSS editor and begin configuring the font, the colors, the spacing and all that from scratch. So let's say you did this. You configured the Normal text and you configured perhaps Heading 1 and maybe Heading 2. You might assume from that, that this would be "good enough". And for many purposes it is.
Then things are going swell in the editor until you choose to apply a Bulleted or Numbered list. BOOM! The styling disappears.
Well, one way to "fix" it, is to just select the list and apply the Normal styling to it. That would certainly make the list follow the formatting of the typical paragraph. But when you do that, it surrounds your list entries with <P> tags. Meaning they will be presented using the same formatting as paragraphs. And you may be perfectly happy with this.
But you may also want your lists to actually appear differently. Perhaps the spacing should be "tighter" with space between list items reduced a lot.
If you were to look at the underlying code for your CSS, you would see that there are likely no entries for UL or OL. And if there are, they are actually lumped together.
So to be in the best possible shape, you need to use the RoboHelp CSS editor (or whatever your preferred editor for CSS is) and define the characteristics wanted for lists.
Special note here. You will often see two different lists in the RoboHelp editor. Only one of those will actually allow you to configure the lists. I'm not sure why the other is even there. Maybe it's a bit of a bug. Who knows.