Oracle SQLDeveloper is designed primarily for Oracle databases. Why do you think it should work for a completely unrelated Sybase database which has completely different data dictionaries etc.?
And why haven't you asked your question in the SQL Developer forum where it belongs? Just because this forum is called "General Questions" it still relates to the Oracle Database in general, and doesn't mean you should post questions about any other product in here.
And let's see how easy it was to find the answer to your question...
1. go to google
2. type "SQL Developer"
3. pick the first link that's returned... Oracle SQL Developer</title><meta name="Title" content="Oracle SQL Developer"><meta n…
4. read the text...
Oracle SQL Developer is a free integrated development environment that simplifies the development and management of Oracle Database
Was that really so hard?
You can use third party jdbc drivers for this:
I've used it for sql server but it should work ok for sybase too.
Integration wont be that good though, only basics will likely work.
Part of their mission is to help people migrate from other DBs:
"Oracle SQL Developer is Oracle's Migration tool to migrate non-Oracle databases to Oracle. Migrating with Oracle SQL Developer reduces the time, risks, and financial barriers involved in migrating to the Oracle platform."
I wish they were focused 100% on their existing customers, but you can't blame Oracle for trying to recruit more licences.