Yeps, works for me, too. I'd still recommend to use the board handle and send out of dialog messages to be independent from call load. Also, please note that you can send as many simultaneous MESSAGE requests as many channels you have licensed and opened.
If you need to process inbound SIP MESSAGE, don't forget to send IP_MSGTYPE_SIP_MESSAGE_OK or IP_MSGTYPE_SIP_MESSAGE_FAILED to complete the transaction and free up the resource.