XMLDB - Nodes to Rows
I found the answer myself after reading through loads of documentation from Oracle. The answer comes in two parts.

First, my original question can be solved by using XMLTable:

SELECT 
  x.ID            AS "MEASUREMENT_ID", 
  x.GUID          AS "MEASUREMENT_GUID", 
  a.COLUMN_VALUE  AS "MESSAGE"
FROM SPERF_XML_RAW x,
  XMLTable('/PerfInfo/EventLog/EventRecord/@Provider'
            PASSING x.DATA_XML) a;


Note that COLUMN_VALUE is a pseudocolumn that can be used in conjunction with XMLTable

As additional information I would like to add the following. You can create multiple columns with the following syntax:

SELECT 
    x.ID,
    x.GUID,
    res."Provider", 
    res."TimeCreated"
FROM SPERF_XML_RAW x,
    XMLTABLE('/PerfInfo'
      PASSING x.DATA_XML
      COLUMNS 
         "Provider"     VARCHAR2(32 CHAR)   PATH '/PerfInfo/EventLog/EventRecord',
         "TimeCreated"  TIMESTAMP           PATH '/PerfInfo/EventLog/EventRecord') res;


But Oracle will throw ORA-19279: XPTY0004 when one or more columns return multiple nodes.

ORA-19279: XPTY0004 - XQuery dynamic type mismatch: expected singleton sequence - got multi-item sequence
19279. 00000 -  "XQuery dynamic type mismatch: expected singleton sequence - got multi-item sequence" 
*Cause:    The XQuery sequence passed in had more than one item.
*Action:   Correct the XQuery expression to return a single item sequence.


The solution to THAT problem can be found below:

SELECT
  x.ID              AS "MEASUREMENT_ID",
  x.GUID            AS "MEASUREMENT_GUID",
  res."TIMECREATED", 
  res."LOGNAME",
  res."LEVEL",
  res."ID",
  res."PROVIDER",
  res."MESSAGE"
FROM SPERF_XML_RAW x,
   XMLTable('/PerfInfo' 
      PASSING x.DATA_XML
      COLUMNS
        "EventRecords" XMLTYPE PATH 'EventLog') rec,
   XMLTABLE ('EventLog/EventRecord'
       PASSING rec."EventRecords"
       COLUMNS
        "LOGNAME"         VARCHAR(32 CHAR)      PATH '@LogName',
        "ID"              NUMBER                PATH '@ID',
        "LEVEL"           CHAR(1 CHAR)          PATH '@Level',
        "PROVIDER"        VARCHAR2(128 CHAR)    PATH '@Provider',
        "TIMECREATED"     VARCHAR2(32 CHAR)     PATH '@TimeCreated',
        "MESSAGE"         CLOB                  PATH 'text()') res;


This will probably fail once more as soon as your document has too many levels, and I have not included a document with namespaces, which will most likely cause this to explode as well.

All information was found in the XML DB Developers guide: https://docs.oracle.com/cd/B28359_01/appdev.111/b28369/xdb03usg.htm#g1055369