Is there a way to hook into the HSL functioanlity with iRulesLX so that I can have a common logging framework when moving to/from TCL and Node?
HSL functionality is not yet available in iRules LX, but it is being worked on. For the time being, you can log locally with console.log if the logging is on the lite side (like the occasional status or error message). These logs will end up in the file "/var/log/ltm" but are subject to throttling (more about syslog throttling here). If you are on TMOS version 13.0, you can have logs go to a dedicated log file per node process.
If your logging needs are substantial (like logging per connection or request, etc.), I would suggest one of the more popular NPM modules that supports a syslog transport method.
I posted a second question on how to use the Log Publisher option with 13.1