Good question. The difference can certainly be a bit vague, even working within a structure that uses both. Answering here since a tweet won't cover it.
I've heard the terms Technical Designer and Creative Designer used a fair amount, but I'm going to avoid the term Creative Designer. I don't like what it suggests, as all designers need to be creative. In the contexts I'm most familiar with, I'd probably refer to them as Technical Designers vs. Content Designers or System Designers vs. Content Designers. None quite cover it, since the cut really isn't that clean.
Technical Designers typically deal more with numbers, systems, and scripting. They're often working on things like class abilities or enemy tuning, which require heavier emphasis on custom scripts and numerical balancing, or with large systems like rewards or itemization, which can often require extensive use of spreadsheets to effectively plan and implement. At times, some types of them also interface with engineers a bit more directly to bridge the gap between designer scripting and fully implemented engineering features, leaning on their understanding of how the technical back-end works to talk the right language. Most of these roles still benefit greatly from a good creative mind.
Content designers, as I refer to them, are typically far more focused on creating an in-world experience. Telling a story, crafting an encounter, evoking a feel with a space. They sometimes have to be technical by necessity, particularly if they're working on a team without strong tools, but numbers, balance, and scripts are all secondary to crafting compelling moments. They will often spend more time planning the "flow" of an experience, thinking about the backstory of the characters involved, and brainstorming ideas for how to awaken a specific fantasy. They'll typically be more involved with dialogue, writing, and where applicable, voice-over.
There's a lot of cross-over in the skill sets of both roles, particularly on smaller teams that can't afford to specialize heavily. And even on a big MMO team, an Encounter Designer might reasonably be somewhere directly in the middle of these 2 labels, as they do a lot of creative planning, care a lot about the fantasy and feel, but also typically need to script very custom sequences that are balanced well against specific player-power levels.
That's how I'd put it anyway. This is definitely an area where mileage will vary from studio to studio and team to team.
[My thoughts and opinions are my own. They are not those of Blizzard Entertainment, and they do not necessarily represent Blizzard design philosophies.]