HSV1 can be transmitted through any oral contact as can HSV2.  With regards to wearing a condom - it is the singular most effective barrier we currently can recommend to people and you should use it everytime you have any kind of sex (oral or otherwise).  That being said, you can have active lesions in the genital area that won't be covered by a condom, so that is why experts say it's the best protection but it is not 100% effective everytime.  You might also have an exposure when you think the person is "lesion or rash free" - but even though you are not seeing physical signs of an active  recurrence - they may have a viral titer and active virus when you decide to have sex - and you are then at risk.