I see two problems at the moment, offhand:
First, when you construct your DirectEntry, you don’t seem to be setting a position, meaning that it presumably ends up at (0, 0, 0). This is fine under “aspect2d” or “render2d”–but not under “render”, or a least, not under the default conditions of render.
You see, the default 3D camera is also located at (0, 0, 0), and thus, presuming that it’s not moved, anything placed there is too close to it to be seen.
Your DirectEntry might thus become visible if you move it along the y-axis by some distance; how far I’m not sure offhand, as I don’t know the default size of a DirectEntry in world-units.
The other problem is that, as you’ve found, I believe that DirectGUI objects only by default work properly when parented below aspect2d.
A quick search turned up this old post–I don’t know whether it’s still accurate, but it may be, and it offers some information that might aid you in getting your DirectEntry to work:
Now, I wouldn’t be surprised if the default MouseWatcher is fine in your case, as you’re not creating a new window.
However, it may be that what you’re lacking is a “PGTop” node.
Conversely, a little more searching turned up the neat trick described and shown in this thread: