I had a somehow related discussion on the main network wide meta site. Here is the link:
Zalgo in user names and effects on comments rendering
As you may see from Mark Gravel comment:
I'm pretty sure this is by-design; until there's actual evidence of a genuine problem (that isn't solved simply by communication), I'm not sure there is anything to fix. If there was a change, I would expect it would relate to our increasing internationalisation
The staff currently prefers to handle such situations manually, since the cost of a full-fledged fix doesn't still seem to be worth for the actual benefit.
That said, this doesn't mean that abuse should be tolerated. While there are some cases where unicode may fit (a comment about Cthulhu written using Zalgo fonts may be funny if done with moderation), one should remember that using unicode harms the site in at least two ways:
breaks the site layout (see any Zalgo post for an example
adds noise to search (obviously, you cannot search normally for words that were written using Zalgo or other unicode fonts).
Based on that, I agree with Skooba - abuse should be dealt with, either by editing if possible or by resorting to flagging if no other option is available. Just remember that this is a weird topic with no general agreement, so try to explain your reasoning in the custom flag so it doesn't get dismissed as it already happened to you.
I just found out that this post on the main Stack Exchange network meta states that:
Abuse of the system or community is everything that is created with the intention to harm them. This includes posts that contain no useful content at all – i.e. gibberish posts along the lines of:
Cats are not allowed to walk across keyboards as part of Stack Exchange posts; this is abuse and should be flagged as such.
Such posts are deemed worth of a rude/abusive flag. By extension, I think that content written with Unicode characters or symbols-based substitutions should be handled in a similar way (BTW, I would wonder how those look like while using one of the available smartphone apps).