CAD tip # 12306:

(defun isRunning? (procname / apps item lst meth1 meth2 WMI)
  (setq WMI (vlax-create-object "WbemScripting.SWbemLocator")
        meth1 (vlax-invoke WMI 'ConnectServer nil nil nil nil nil nil nil nil)
        meth2 (vlax-invoke meth1 'ExecQuery "Select * from Win32_Process"))
  (vlax-for item meth2
    (setq lst (append lst (list (vlax-get item 'CommandLine))))
  )
  (vlax-release-object WMI)
  (vlax-release-object meth1)
  (vlax-release-object meth2)
  (setq lst (vl-remove nil lst))

  (vl-some '(lambda (s) (wcmatch (strcase s) (strcat "*" (strcase procname) "*"))) lst)
)

For the procname parameter, use any substring identifying the runstring of the specific application or process - e.g. the parameter "acad.exe" should always return T, as AutoCAD is running for sure:

(isRunning? "acad.exe")

Is the Windows indexing process running?