Did Exporter ever die or issue a warning when it clobbers existing symbols? I think it should 
$ perl -MData::Dump::Streamer -MYAML -le ' Data::Dump::Streamer::Dump(
+ \*Dump ) '
$GLOB1 = \*::Dump;
*::Dump = sub {
            package YAML;
            use warnings;
            use strict 'refs';
            my $yaml = 'YAML'->new;
            $yaml->dumper_class($DumperClass) if $DumperClass;
            return $yaml->dumper_object->dump(@_);
          };

$ perl -MData::Dump::Streamer -mYAML -le ' Data::Dump::Streamer::Dump(
+ \*Dump ) '
$GLOB1 = \*::Dump;
*::Dump = sub {
            package Data::Dump::Streamer;
            use warnings;
            use strict 'refs';
            my $obj;
            if (blessed($_[0]) and blessed($_[0]) eq 'Data::Dump::Stre
+amer') {
              $obj = shift @_;
            }
            if (@_) {
              if (defined wantarray and not wantarray) {
                $obj ||= 'Data::Dump::Streamer'->new;
                $obj->_make_args(@_);
                return $obj;
              } else {
                $obj ||= 'Data::Dump::Streamer';
                return $obj->Data(@_)->Out;
              }
            } else {
              if ($obj) {
                return $obj->Out;
              } else {
                return 'Data::Dump::Streamer'->new;
              }
            }
          };

$ pmvers Data::Dump::Streamer YAML Exporter
Data::Dump::Streamer: 2.09
YAML: 0.70
Exporter: 5.63

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In reply to Exporter collision detection by Anonymous Monk

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