nothing more than others
Although all existing answers are right, saying that this sentence is semantically correct, as native I feel like it is not a sentence I would use.
Since you are asking about usage, I would have probably been annoyed by this potential contradiction.
what I would have use
C'est sûr que les garçons risquent de s'y sentir les bienvenus.
I would prefer to explain the guarantee by using:
C'est sûr que les garçons s'y sentiront les bienvenus.
Or, if you rather want to underline the chance it is not sure:
Il y a un risque que les garçons s'y sentiront les bienvenus.
I'm curious, did you find this sentence in a book or have you written it?