Safe in the context of
1. Data theft
2. Data corrupted
For 1 you are nowhere sure. There is also the moto "It is not the cloud. It is someone else's computer." That is why you have to backup your files in password protected rars.
For 2 if you use S3 there is hashing so you know that the file was uploaded OK. Afterwards there is the VPS provider's backup service. I, as a measure of extra safety, I keep the same backups also in an other external detouchable SSD disk.