i cant confirm,
i did a fresh 10.10.4 installation on MBP late 2009 with an Samsung EVO 840-series 500gb SSD and updated 10.10.4 with latest 2-3 updates (RDP , iTunes etc.) and then installed just 10.3.2_MP9 on it. after installation i tried without rebooting to encrypt the HDD which failed with a common 11xxx or 12xxx error (cant remember). i did reboot and then wasnt able to proper boot into MacOS , just a white blank screen.
pressing ALT before the mac-chime went into preboot area of MacOS with only 2 same-named partitions. unfortunately i hadnt a recovery partition for 10.10.4 so i wasnt able to ALT/CMD + R and so i resulted into a complete clean reinstall of 10.10.4 .
while Releasenotes doesnt state 10.10.4 to be official supported, i just wait until MP10/august 2015 or MP11 (september/october) will be released
let's see ;-9