Yes, it's possible to do TCP Connection Test without login into DataPower box.
In general, DataPower has provided TCP Connection test UI feature on it's WebUI. After login to DataPower box, click on "Troubleshooting" on control panel and you will get option to try TCP Connection Test to any IP and Port combination from DataPower.
But it's not a very viable solution specially when you have multiple boxes in production. You need some easy way out test TCP Connection without login to DataPower box.
SOMA Interface can help us here. You can write a SOMA script to request DataPower to confirm TCP connectivity.
This is the Sample of SOMA Script..
<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:man="http://www.datapower.com/schemas/management">
<man:request domain="DOMAINDEV"> <!-- Replace domain name -->