I don't know if I understand your question, but you could grab the vgname and stick it in a variable like $now_vgname, and do the same with the label and then build your hash when you get the id. EG

...
my ($now_vgname,$now_label);
while ( <$input_handle> ) {
    if ( /lsattr -El (\w+)/ ) 
        $now_vgname = $1;
        next;
    }
    if ( /label\s+([\/\w]+)/ ) {
        $now_label = $1;
        next;
    }
    if ( /lvserial_id\s+([\w\.]+)/ ) {
        $host_info{VG}->{$now_vgname}->{$1}->{LV} = $now_label
        next;
    }
}
[download]

This code is just to demonstrate the idea, it probably won't work as is.

--Pileofrogs