We use the cross over cable for directly connecting the device to the pc to access the web UI. But during deployment do they still need a cross over cable or a straight cable will suffice?

The cross cable connection was used for the troubleshooting purpose in case of there was a network issue reported at the device under the client's network environment.

In real case,the device is just like other network equipment e.g.network printer that can connect to the LAN via the straight cable.