Looking at the "code" you're running in ArcSDE, it looks like FME isn't registering the layers with ArcSDE properly. By running the delete and then register you're rectifying this by removing the previous registration and then manually creating a new one.
You've not provided enough information to diagnose the problem further (hence everyone asking questions of you).
In theory it should work. This document has basic information about the writer: http://fmepedia.safe.com/articles/How_To/Comparison-of-FME-readers-and-writers-for-SDE-and-Geodatabase
Full information about the writer can be found in the Help -> FME Readers and Writers Reference.
I can't test this writer, but the table registration code should probably be in the log. Check to compare the code in the log with the code you're using yourself in the ArcSDE console.
Note: your tables can only have a single geometry type in them for successful registration