Why not? It's every bit as functional as the planner in Frozen Synapse, although different in some respects.
For example synchronised roomclearing is done with the Alpha, Bravo, Charlie and Delta commands, while in Frozen Synapse you have to perfectly calculate a countdown timer for something to be perfectly synched.
But in general they are very much alike, except for the fact that Rainbow Six had multiple-stories buildings with stairs and such (would be cool in Frozen Synapse too maybe, though very difficult to properly implement i guess

).
Anyways, nailing down a mission plan in Rogue Spear for example was more fun to me then it is in Frozen Synapse, but most of that has to do with believability. In FS you control single units and have them do seperate things, while in R6 you control fireteams and such.
Which is my biggest gripe with FS: though highly tactical, the tactics arent very realistic. Roomclearing as a fireteam just isnt needed, because units function as single entities. You can make them work together, but the random generated situation hardly ever calls for it.
It's hard to describe exactly though. However i would love something like a SWAT mod for Frozen Synapse, where units function as a team ala oldschool R6.