That type of tulip will stay open if a ball enters from above. There is a tiny ramp inside behind where the sticker is. The ramp "bumps" the ball towards the rear of the tulip...causing it to miss thelever that closes it. A ball from the side will close it.
I have seen many pics of the sumo wrestler machines. However, I never paid attention to the part above the wrestlers. So I do not know what is common or normal for it. That being said...many machines having the same center have other features on the playfield different. From your pics I believe it was made that way. Although the holes do look like they line up with the mounting holes for the "face", I don't see any "dirt or fade lines" in a round shape where the "face" would have been. Also, I don't think that the removed nails prevent the dangling things (I think they are called jellyfish) fron swinging open...like a hanemono (wing type). If I am not mistaken, hanemonos are not vintage machines. I believe they began with early moderns, as they are electrically operated.
That paragraph was because you stated "the nails removed would hold them in". If you touch one of them, it should swing back and forth, pivoting at the top. If the nails would hold them in, and prevented the balls from entering the center, they would need to pivot at the bottom. Plus there would have to be some kind of mechanical linkage to operate thwm. Not to mention whatever device to activate them. Like you said...nails blocking them would not make sense. Looks to me that they were removed to make jackpots easier. Never mind...I just looked at an enlarged pic, and if the nails were there...they would make a spot where a ball could get stuck. Now I am confused as well!