Sometimes. Other times those chars are not allowed in the embedding context (paths, for instance), so you have to use '+' and ','. Or maybe '_' and '-'.
If you follow rfc4648, those are "base 64" but not "base64":
> This encoding [using '-' and '_'] may be referred to as "base64url"... Unless clarified otherwise, "base64" refers to the base 64 in the previous section ['+' and '/'].
> This encoding [using '-' and '_'] may be referred to as "base64url"... Unless clarified otherwise, "base64" refers to the base 64 in the previous section ['+' and '/'].