So - How Does Marvel Get Inhumans and SHIELD To Meet?
Of course, Agents of S.H.I.E.L.D. Season 5 and Inhumans have more in common than the universe they exist in. In addition to the fact that they deal with Inhuman affairs, both take place off-Earth. That is to say, Inhumans takes place at least in part on the blue area of the moon, away from prying human eyes, while S.H.I.E.L.D. is headed to space. While this could be coincidental, it also opens the door for the established S.H.I.E.L.D. team to come in contact with this secret Inhuman society.
After the events of Inhumans, Earth will inevitably be aware of the Inhuman Royal Family. After all, it's a little difficult to ignore the giant teleporting dog and his mute master appearing in the middle of a busy intersection in Hawaii. As such, it's surprising that S.H.I.E.L.D. doesn't react to this Inhuman incident at all (as indicated by showrunner Scott Buck, who promised there is no crossover as yet). This calls into question Inhumans' timeline. If S.H.I.E.L.D. isn't around to deal with these wayward Inhumans, they must be preoccupied in some way -- whether by Aida's machinations or their off-planet adventure, we've yet to see.
If you tuned in for Agents of S.H.I.E.L.D. Season 4, you'll know that things went south pretty fast when Aida started to show some signs of independence. She went on to create Life Model Decoys (LMDs) of each member of Coulson's team and charged them with some nefarious tasks, which resulted in the destruction of S.H.I.E.L.D. headquarters. Because the LMDs looked just like the ensemble show's main characters, Coulson and his team were implicated, in particular by their government liaison Brigadier General Glenn Talbot. Talbot ultimately got a bullet to the head by Daisy's's LMD in a room full of government agents, further tarnishing the team's reputation.
Considering that, it certainly wouldn't be surprising if the events of Inhumans went down at the same time as the last few episodes of Agents of S.H.I.E.L.D., which the team spent fighting LMDs when they weren't trapped inside the Framework. S.H.I.E.L.D. would have been far too busy to deal with a few rogue Inhumans in Hawaii, not to mention the fact that they're now considered outlaws by the US government. However, these Inhumans events could very well explain one of the mysteries from the Season 4 finale: the diner scene.
After Coulson, Daisy, May, Fitz, Simmons, Mack and Yo-Yo defeated Aida with some help from Ghost Rider, they headed to a diner and waited for the government to come for them. As they were about to order dessert, the electricity in the diner went out, only for a white light to blare just outside the windows. The sound of radio chatter filled the silence, and the weary agents raised their hands to surrender as men with tactical gear and guns flooded the diner. A bald man in a suit stopped directly behind Coulson, confirmed Coulson's identity and pulled out a glowing green device that froze Coulson's team where they sat. "The window closes in less than two minutes. Take them," the suited man said -- and the next time we see Coulson is in space.