As long as you conform to the 150 users, 300 devices, etc. rule you should be okay. The solution overview mentions adding a second for redundancy...
https://www.cisco.com/c/en/us/products/collateral/unified-communications/business-edition-6000/solution-overview-c22-734271.html
Built to grow and evolve with your business: We’re living in a world of constant change, and Cisco BE6000S is designed to scale up as new business needs develop. It supports up to 150 users and 300 devices across multiple locations. We support further growth through seamless migration to our Business Edition 6000M and Business Edition 6000H models (BE6000M and BE6000H), which allow you to smoothly scale to 1000 users, 2500 devices, and 100 contact center agents when the time is right. Each BE6000 platform model is designed using a simple, single‑server approach that fits businesses with limited IT resources and budgets. You can also add a second system for redundancy to help ensure business continuity and provide additional peace of mind.
