Condoms are very responsible protective measures for preventing the transfer of most STD’s however with genital herpes; some of the areas that are affected with the blisters (outbreak) may still be exposed as the condom may not cover these areas fully. This may then allow for the spread of the herpes virus (spread via skin-on-skin contact).
Sex does come with a multitude of risks so it may be best to have both yourself and your partner tested before taking the risk.