Hiding parting lines is certainly possible, but it’s tough and just requires a lot of control of the tool.
For rotational molding, and when working with large tools that becomes quite a bit harder since you have a lot more metal, and a lot more risk that something won’t be perfect and flash will occur.
The top image is definitely a rendering, and the bottom one you can see the parting line. Seeing the parting line that results due to your draft angle is more likely than worrying about flash, but painting the part after the fact can help a bit.
Ultimately anal control for something like that is going to depend on your tooling vendor. If you show up to most tooling vendors and tell them you want a gigantic rotomolded part with no seams they may tell you itll be 5X the normal tool cost, or laugh you out of the building. This is why when you read about Apple suppliers so many of them refuse to work with them after a project due to the insane requirements that most customers don’t demand.