Can you have a single BL & AR company and have transactions post to more than one GL company?

The short answer is no.

However, there are some creative ways to accomplish having a single BL & AR company and still booking information to various GL Companies.

Option 1: Using allocations and getting creative with your Process Levels and possibly accounting units, you can move the amounts to various companies using the allocation module.

The AR process Level setup has a default accounting unit that allows you to book all transactions for this process level to the various accounting units and then setting up an allocation to transfer those amounts at the end of each period would allow you to see the AR amounts on your various GL companies in the financial statements.  I would make these allocations auto reversing so that you can show what you need to for financial reporting only.

Option 2: Setup the various AR and BL companies and use the National Account relationship for your processing.  This option will allow everything to book in the correct company, and still allow you to process payments and adjustments, produce various reports, create consolidated aging reports and all other AR reports.

So as often is the case, you can get what you want, you just need to think it through and see if it will work for your needs.