Add 2008 R2 Certificate Authority to 2008 Environment?

Hi,

Apparently Microsoft Direct Access One Time Password (OTP) issuance requires the use of a Certificate Authority that runs 2008 R2 or above. The problem is that our Certificate Services environment is all 2008 (One offline Root CA, one offline Policy CA and four online issuing CAs). Would it be at all possible to add an additional 2008 R2 CA to the environment without harm?

Thanks!

Patrick