True. Oda did not make it obvious.
However, Blackbeard is aware that Luffy and the new generation are in Wano with Big Mom chasing them. Its safe to bet that Blackbeard knows about the Poneglyphs, and the reason why they are fighting there. After the end of the warlords, Teach is clearly going somewhere. He could literally use this opportunity to take out one of the other emperors when they are weakened by the battle and take the Poneglyphs with him. Its dirty but Its something he would do based on his past actions.
The name of Blackbeard pirates' ship is called the Saber of Xebec. The captain of the Rocks crew was Rocks D Xebec and he started this crew on Hachinosu island which is the exact same place where BB is creating his Pirate heaven. As Van Auger said, there is no such thing as coincidence, there's only fate. Blackbeard is very likely connected to the Rocks and he may be his son which explains why he remained hidden from the WG thanks to WB, and is using an alias. Worst case scenario what if Teach intends to revive the Rocks Pirates by allying himself with Weebil (new Whitebeard), Big Mom, and Kaido to take out the Straw Hats.
Its very unlikely this will happen but if it does it will completely elevate Wano into a legendary arc.