Podés hacer algo como esto y simplificar el código :)
Código HTML:
<form id="form1" name="form1" method="post" action="#">
<label>
<input type="radio" name="RadioGroup1" value="hombre" id="RadioGroup1_0" checked="checked" />
Hombre
</label>
<label>
<input type="radio" name="RadioGroup1" value="mujer" id="RadioGroup1_1" />
Mujer
</label>
<input name="Generar" type="submit" value="Generar" />
</form>
<script type="text/javascript">
var formulario = document.getElementById('form1');
formulario.onsubmit = function(e) {
e.preventDefault();
var radioSelect = document.querySelector('input[name="RadioGroup1"]:checked').value;
var arrayHombres = ["Carlos","Juan","Antonio"];
var arrayMujeres = ["Ana","Luisa","Carmen"];
var arrayFinal = (radioSelect == 'mujer') ? arrayMujeres : arrayHombres;
var rnd2 = Math.floor(Math.random()*arrayFinal.length);
document.write(''+arrayFinal[rnd2]);
}
</script>
Saludos