Configuring NXLog to support log files containing log lines that span multiple lines can be done by adding something similar to the following snippet to nxlof.conf:
<Extension multiline>
Module xm_multiline
HeaderLine /^<event>/
EndLine /^</event>/
</Extension>
<Input in4>
Module im_file
InputType multiline
# Discard everything that doesn't seem to be an xml event
Exec if $raw_event !~ /^<event>/ drop();
File "C:\\myfile.log"
CloseWhenIdle TRUE
</Input>