Hi Cameron
I think it would be okay to add them to your tree, and then go back and find the information, I personally have a great number of profiles, without the source being added, but as I get to them and then do the research I add the source I get to them then. Just remember to check and see that noone else has already entered your relative as part of their tree, in my case I have come across, at least half a bozen cases, where this has happened and had to ask to be a trusted member to continue the line
Regards Paul