No at all
Experiencing any kind of software using your favorite language is a great way to build meaningful projects
It's just that for me most kind of server editor should use the DOL libraries to be sure they match the server behavior, for example when you'll need to implement Master Level Editor or Champion Level Skills Editor, you'll have to implement the code from DOL in your own Java Project. And as I did wrote Data Career code I can tell you there is some "weirdness" in Master Levels and even more "weirdness" in Champion Level Skills...
There is so much "weirdness" in Champion Level Skills that I will mostly rewrite this code soon enough (especially since new Champion Level Live update have changed a lot of expected behavior from these skills !) and you may have to update all your own Java Code again...
I know this can be frustrating to lose productivity when learning a new language, that we can have some developer preference for specific language/framework/IDE (I didn't wanted to code for DOL at the beginning because of .NET technology, Hopefully Mono gave me a good result with even latest .NET implementation and allowed me to be sure I would still be able to run this project on my own long standing GNU setup !), and above all of this it's pain in the ass when you need 2hours to build something you would have done in 15 min using your "weapon of choice" language
But All this is just a strong Advice, I worked with a skillful PHP developer on Freyad, he used powerful abstraction framework and database search engine extension to build some light server editor project, he got stuck during display implementation, DOL had so much "weird" behavior that he needed to build specific data structure to hold constants matching these behavior and implementing specific code for all of them, on my side I was changing DOL code on a weekly basis, and he needed to change it's own PHP implementation most of time, he finally quit before implementing anything that would allow editing, leaving a well working DOL Object Search Engine
(but totally not the expected result)
To sum up, use any language you like, but you should really try to "bind" on DOL libraries like GameServer.DLL (and doing this in any language could be much harder than just working in C#, but if you can bind DOL in an other language that would be a great job !)