Yes, there is a limit... There can be up to 900 entries in all 15 tables, there is no limit per table as long as the total is under 900, at least not documented.
From the MiVoice Office 6.1 Features and Programming guide, page 249:
The system can have up to 15 call routing tables. There can be a total of 900 patterns in all of the call routing tables combined.