Yes, without sperm there could be DNA. And yes you can have DNA evidence without ejaculation. Sperm on clothing is much easier to detect, even after washing clothing several times it can be detected.
When you're talking about a sexual attack, there is several ways that DNA is transferred and can be found. Fingernails are the first area, fighting the attacker off will cause epithelial cells to be embedded under the nails. Additionally pubic hairs are lost and transferred, without a condom there are epithelial cells left behind from the friction of the assault, the more friction the greater number of cells left behind. This kind of transfer of epithelial cells is called "touch DNA" . Additionally you can have small fissures and abrasions that leave behind blood, sweat, and then there's saliva. Every cell in you body contains your DNA, so think about how many cells are transferred during that kind of contact.