He was a close friend and ally of Lysander and a noted philhellene. That won him many friends among the Greeks; Xenophon was a jingoistic xenophobe who disliked Persians in general with his noted exceptions being Cyrus the Great and Cyrus the Younger. That the younger Cyrus shared an exclusive club in Xenophon's eyes with that most celebrated of Persians speaks to his qualities and his perception among the Greeks.
His relationship with Lysander will very likely make for a strong Laco-Persian alliance; Cyrus had made Lysander satrap of his provinces when he was away. In his victory, Lysander might be put in charge of some of his former satrapies, at least Lydia and Caria*, maybe even Phrygia and Cappadocia. If that were to happen, we'd get an interesting geopolitical limbo with Lysander being a citizen, general and subject of Sparta whilst having a personal empire as Cyrus's satrap in Anatolia. He also allowed those Greek cities on the Ionian coast he hadn't given over to Lysander for his decarchies to have significant autonomy when they joined his rebellion, which will endear him to the Greeks even more.
I think Cyrus might be well-received and well-perceived enough by the Greeks that Sparta's alliance with him won't garner as many accusations of shameful medising. It could actually make the Greeks begin to see Persia in a more positive light, if the good relations and philhellenism last throughout Cyrus's reign and beyond.
As for Sparta, I think she would be much more secure in her hegemony, and we might actually see some peace in Greece for a generation.
*Caria is Tissapherne's satrapy, but given that he had framed him for treason once then went on to warn his brother of the rebellion and fight against him, I think it's safe to say Cyrus won't be wanting him around, freeing up Caria for Lysander to govern in this scenario.