I see no issues with this.
I do this myself, especially if a user has asked bioinformatics-related questions in the past. This was a question about parsing and reformatting a Fastq file from a user with a number of bioinformatics-related questions on our site:
The question was definitely on-topic here but I wanted them to just be aware of the bioinfo site as they weren't associated with that yet. I noticed that they immediately created an account there afterwards.
That way the user has two venues for asking questions and can choose the one that they feel more closely fit their needs.
In addition to that, many over here might not know that there may exist tools for performing certain common bioinformatics tasks and will instead "cobble together" a script that may work for the specific data shown (only), but that does not properly handle "quirky real data" (biology is messy). The user leaves not knowing the limitations and are confused when trying to apply the same thing to another seemingly similar data set and fails.
So from the user's perspective, it's a good thing to be made aware of the Bioinformatics SE site.
It would also, obviously, benefit the bioinfo site to have more users, and by having more users on an SE site in general, further people (colleagues, friends etc.) are made aware of the resources available.
Also, some text-processing tasks that bioinformaticians want to perform on their data are sometimes somewhat dull. It's "get these lines if that value is positive". And then there's another similar question, but on another set of data, possibly in another well known format (in bioinfo circles), but with essentially the same formulation... The solution may be interesting in the ways it performs the task, but it would not in other ways benefit a non-bioinformatician Unix user.
I would not migrate bioinformatics questions to the bioinfo site unless they were explicitly about the specific use of bioinformatics software, or asked about bioinformatics methodology etc.
I would similarly not see any issues with pointing out the existence of the Vi and Vim site, or any other SE site, to users that may benefit from having access other users with special interests/expertise (although I would honestly not think pointing out the Vi site in particular would need to happen that often).