In multiple interviews or answers it's been known that cipsoft employees may play Tibia.
If you want to read more about testing in Tibia I recommend reading this Testers article-
CMs: How much of your daily work do you spend on Tibia?
Testers: Usually, we spend about two thirds of our daily work on Tibia. Though, if it is needed, during peak time.
Here's more answers-
Rejana interview on TibiaGoals-
-I do log in from time to time, I also have a house, but I would not call it playing actively. I have a hunting round I've been on for years now, and I don't really dare to go anywhere else. When a character of mine dies in Tibia, it falls into a great depression and never logs in again. So I have to start over. (Don’t ask, just a personal obsession somehow…)
I've now been on the same character for 4 years, so that's the time frame I've been on the same hunting round – not dying. That’s not actively playing.
We CMs are allowed to play during working hours if time allows it. There are other departments, however, that have to spend time ingame during working hours, since it's way more important for them to be familiar with the game mechanics and playing styles.
Letters to Cipsoft-
As a part of the Tibia Crew, some of us embark on covert journeys from time to time into the very world we've helped shape, playing incognito alongside our players. The idea of a team member possibly being a part of your crew, bravely confronting Tentugly side by side, is as thrilling to us as it is to you. And it's entirely within the realm of possibility!
Some players even got hired by Cipsoft-
Guido, Craban, Mercutio, Chayenne, Knightmare, Grimrath, and Solkrin were all Tibia players first before they were Cipsoft employees.