It is no problem to install both on the same computer. I have done that too and surely also IDM and other users. There are no conflicts.
I only recommend to run a custom installation for both programs because it simple does not make sense to add both programs to the PATH environment variable, to integrate both programs into Windows Explorer and to specify both programs as view source editor for IE.
The program directory of UE and UES should not be added to the PATH environment variable if you never run uedit32.exe or uestudio.exe from a command line prompt without using full path which I guess you will never do.
The shell integration into Windows Explorer makes mainly sense with both programs installed for UltraEdit, not for UEStudio which is mainly for working with projects and not quick editing of text files as UltraEdit. This also the reason why I recommend to specify only UltraEdit as view source editor for the Internet Explorer.
If you want to save some disk space you can also uncheck in one of the 2 program installations the installation of the dictionaries for the spell checking feature. You can specify in the configuration dialog of UES and UE the directory with the dictionaries. So it is possible to install the dictionaries for example with UltraEdit and specify in the configuration dialog of UEStudio the Aspell directory of UltraEdit.