Read the paticular sites terms of use if y ou have any concerns as to what the appropriate use for the music is. If they dont have it contatct the owner of said music and find out. If they dont reply dont assume that they dont have rules. Non reply doesnt mean free to use in any way you want. The term royalty free usually means that you dont have to pay to use the music but its just a term. Find out what you can use it for if you really worried about it. Releasing a free title would be alot safer and if you have any doubts, (cant contact anyone, find terms of use.) at least give them credit.
Just some thoughts.