AB has a tech-note in their knowledgebase that has a sample program to extract the datalog from a micrologix 1100 using a compactlogix or controllogix PLC via Ethernet, using a MSG (message) instruction. This would mean it should be possible to sniff the traffic to the micrologix and decipher the handshake used to grab that data from the PLC. You could then write the code in ignition to replicate that handshake. Otherwise, you will have to pull the datalog into a compactlogix or controllogix PLC and then pull it into ignition or stick their proprietary datalog upload tool on your ignition server and somehow automate it.
Personally, I don’t see any way to do it that would be worth the time required, but I don’t know your application. Sorry I can’t be more help.