It is my understanding that the dump collector "transmits diagnostic information to a remote netdump service, which stores it on disk," to paraphrase a VMware KB article. The netdump service saves the diagnostics in the "zdump" format. It's been a few years since I did ESXi administration, so I have no idea what the file format really is.
But here is the thing. If the dump collector runs on Windows or Linux, and writes its file in some text format on a local disk => then you can install the Splunk Universal Forwarder (UF) on that server and collect the files from disk and send it to Splunk. So just find out where the vCenter guys are going to store the months of data, and collect it from there. Your UF will only need to run with sufficient privileges to read the files.
Although I expect it is possible for Splunk to monitor the ESXi Dump Collector service directly, I would not want to do that - partly because it might interfere with what the vCenter guys want to do. But mostly because it will be easier to pick up the logs files after they have already done the collection for you.
