Absolutely, it's OK to rest when you like. We do have people who start while they are still undergoing treatment and people like me who try to continue through any further treatment. On race days, we like people to be fit enough to keep going if possible, but on training paddles you do what you can. And we have the 'princess seat' at the front of the boat where the drummer sits on race days. I'm sitting in that in my profile picture, as it was taken less than 4 weeks after my mastectomy and TRAM flap surgery, when I couldn't paddle but went out for the ride.
Viv xxx