The reason why you are likely obtaining no data in the View Data Points web page is that you have not entered the correct parameters for the data point properties. As far as I can tell the physical transceiver interface parameters have been setup correctly or at least the ilon Modbus driver has been set to one of the supported bit rates, number of data bits and stop bits that the device is capable of supporting. The actual setup is down to you.
The format of the datapoint that represents the L3 phase voltage would seem correct at a UNVT_float. You have used the 32bit register format. If this is correct the lengths should be 4 bytes as you have shown but the stop address should be 7515 and not 7516 as shown. You might try the 16 bit register format in which case the start address should be 6028 and stop address 6030. You might need to also look at changing the format of the datapoint to something else other than UNVT_float. in my experience most Modbus variables on an ilon are formated up as an unsigned quad.
After checking the above you should then go back to the View DataPoints web page and see if the values you obtain look anything realistic and resemble the actual values that are shown on the front panel display.
if this is the only piece of data you wish to monitor then consider putting a lower number for the max elements. Setting a value of 255 means up[ to 255 datapoint values are retrieved at any one time meaning you migh not get the databack in the time allowed which will mean the datapoint will be shown off line.
If the Smart Server version works then consider upgrading your E3 plus to the smart server version. The latest smart server build is 4.06.057. The Modbus driver is much more comprehensive on smart server and the console ouput can be used to debug read failures