When operating (3) of the 61605’s in 3 phase mode can the Phase angle between phases be programmed for phase angles other than 0, 120, 240 Degrees?

YES, the Phase angles can be set independently for each phase see 61605 model ac power source User Manual sections 3.7.2 & 3.7.5 for manually setting the Phase Angle Degrees, see section 7.6.2.5 for instructions on using the SCPI commands for programming and using the remote interface to set the Phase Angle Degree. This is also applies to the 61601, 61602, 61603, & 61604.