Valve recently announced that the qualifiers for TI5 will be held in the second week of June, which means it will clash with DreamHack Summer and perhaps even ESL and MLG.
But as of now, the scheduling conflict isn’t something that’s worrying for the swedish arrangers.
– It’s in everyones’ interest that there will be no scheduling conflicts, but it’s too soon to say how this will affect Dota2 at DreamHack Summer, Dreamhack Head of PR Fredrik Nyström says.

According to Gosugamers, Valve announced the qualifiers for TI5 via mail just the other day. They will be played during the second week of July whichs means it will take place during the same time frame as DreamHack Summer. But since the format of DHS isn’t set yet, the arrangers aren’t worried by the news.
– We always talk with the publishers about dates. Dota2 is an important game for us and we have no plans on not having it in the lineup. It’s in everyones’ interest that there will be no scheduling conflicts, but it’s too soon to say how this will affect Dota2 at DreamHack Summer, Fredrik Nyström says.

At least one Dota2 tournament will take place during DHS, since the Swedish Championships ESPORTSM added the game for 2015, replacing last years MOBA League of Legends.