I believe there are few gay bars in Helsinki actually. Here is a list of some of them:
You mentioned the most popular DTM already and then there is one called Hercules in the city centre also, but mostly men go there. It's the biggest gay club in the North and they use their own disco money which is kinda cool i think!

There is a beautiful park called Bear park in Kallio (an area near the Helsinki city center). One of the most popular gay events -DBR drag bear race is held, during the awesome Helsinki Pride (I warmly recommend you to take part in that event). In the park there are two gay cafes Bear park cafe, and Bear park Kulma, which are open for all kinds of people.

If you are into arts, you should visit Cavalier. It's a small place where they have art exhibiotions and shows as well as music events and gay parties called "Otso party".

The newest gay bar in Helsinki, BLVD Room, is specialized in wines. I haven't been there but I've heard they have some fine wines and the atmosphere is cozy, so check the place if you are interested in wines.

All in all Helsinki and most of Finland is a gay friendly and tolerant place, so the bars and cafes are open for all kinds of people no matter if you r lgbt+, straight, black or white, short or tall.. So basically feel free to go anywhere and if you aren't treated nicely it's probably not because of your race or sexual orientation etc., but just poor service or typical Finnish sulkyness. Altough in general we are nice, I promise!