Calling extproc dll from native Webservice

We have a PL/SQL package in Oracle 12.2 on Windows that calls an extproc dll from Esri (st_shapelib.dll). When we use the function in the database it works fine. But we have to call it via an Oracle Native Webservice. We test the webservicecall with SoapUI, but we don't get a result from the function and no error message. The process Oracle.exe don't respond and remains in status Active until we kill the process. Other webservices, that don't call an external dll are working fine. So my question is, is it possible in general to call an extrproc dll through