Side-scrolling a Table is Fine
There’s nothing wrong with side (horizontal) scrolling of tables. Users of Excel do it all the time. You just need to have fixed (non-side-scrolling) row headers to identify the rows no matter where the user has scrolled in the table. That is, the table should by default have “frozen panes,” to use Excel’s term.
Like maps, Gantt charts, and various other forms of data visualization, tables are inherently two-dimensional. It's best if these visualizations use a simple, standardized, and consistent way to view content horizontally and vertically. Building for horizontal scrolling allows users to set the window size to what they want for their conditions, rather than forcing them to adopt a width you've dictated.
Side-scrolling Prose is Not
The rule against horizontal scrolling in web sites applies to prose not tabular content. Making users scroll sideways to read each line in a paragraph makes for a lot of scrolling around, which is a pain. It also can make it difficult to print out the content in any reasonable readable way. You also, obviously, wouldn’t want users to have to scroll to the right to find a side bar menu or other key controls or content. That’s not where users expect the sidebar menu to be. What they expect on the right is irritating animated advertisements to be avoided. But, again, that's only for prose-oriented pages, not tables.
Your main challenge is to make the availability of side-scrolling obvious to the users. Because it’s underused in web apps, users may not think to look for the horizontal scrollbar. Users are used to doing the F-pattern scan of a web page, which means they could miss the scrollbar which tends to be in the bottom right. It may be sufficient to borrow a mobile technique of truncating the rightmost column to signal there’s more to see beyond the right margin. That could prompt users to look specifically for the usual a control to move sideways. Testing would help you find what is necessary.
That said, there are alternatives to side scrolling that may be better in your case. You’ll find them in the answers to a more general form of your question at Best way to display more table columns and rows than I have room for? As a first-cut, estimate which alternative means the least clicking and dragging for your users for their typical tasks, and make that your prototype for initial testing.