I use my swap partition for both maemo and mer. You might have forgot to select the swap partition during the installation. Mer ask you twice about swap. First during installation when you were selecting what partition to install mer it also ask you what partition you want to use for swap. So then after the installation is done and you have rebooted your device to mer booting for the first time, it will show you your swap partition that you had selected and ask you to enable it. After that it will be set.