How about this:

sub normalize_date
{
    my $date_proto = shift;

    my $stringified = "$date_proto";

    # Check to see if it's NOT a reference
    unless ($stringified =~ /\(0[Xx]\d+\)$/)
    {
        return split /\D+/, $date_proto;
    }

    # At this point, we know we have a reference of some sort ...

    # Let's see if it acts as an array ...
    if ( eval { @{$date_proto}; 1} } )
    {
        # We know we can treat $date_proto as an array
        return $date_proto;
    }

    # At this point, we don't know what to do with $date_proto.
    # (Well, the OP hasn't spec'ed it out ...)
}
[download]

The major update here is that it plays nicely with overload. For example, I might have:

package Date::As::Hash;

use overload '""' => 'stringify';

# Some stuff here ...

sub stringify
{
    my $self = shift;

    "$self->{MONTH}/$self->{DAY}/$self->{YEAR}";
}
[download]

I wish HTML::Template would do something like this ...