what are the checksums surrounding keywords in the SQL generated by WP_Query and do I need to use them too?

It is literaly a place holder and not a checksum and it indicates what part of the query should be converted to % before executing the query. (this is done to harden security)

I do not see right now an easy way to fix the preg_replace that the codex suggests as I suspect this place holder might be “randomly” generated, but if you just want to search for the same term that is being searched for in the rest of the tables you can get the term from the WP_Query object and make the replacement code much easier to write as you will not need to extract the term from the query itself.