Just because a submissive has a safeword doesn’t mean as the Dominant that you aren’t allowed to check in with them to see how they are during the scene, or that you can just rely on the submissive to tell you if the play gets too much. The Dominant is responsible for the submissive during the scene, and should be watching body language for visual clues on how the submissive is finding the play. The Dominant also needs to use their judgement whether the submissive has had enough, e.g. if the submissive asks to carry on but is uncontrollably shaking, or asks to be caned harder but is already bruised and bleeding. It is not enough to simply say afterwards the submissive didn’t safeword so it wasn’t your fault.
If the Dominant wants to check in with the submisive during the scene to find out how they are finding it, this is also perfectly acceptable. This is why some people like the traffic light system so much as the submisive can respond with green to carry on exactly as it is, amber if they feel close to a limit or would like a small change, or it reminds them they can call red if it’s got too much but their brain was so lost in the moment they forgot they had a safeword. There are other ways to find out how someone is doing, such as during a caning scene, ask the submissive to choose a number of hits between 1 and 10. If they choose 1 you know they are close to having enough, at least of the cane, if they choose 10 you know they feel they can take a lot more. Checking in doesn’t need to be just asking how someone is and breaking the mood of the dynamic.