In SD-SDI mode, the rxoutclk of the GTX RX is not really a recovered clock because the CDR unit is locked to the frequency of the reference clock, not to the SD-SDI serial stream. The only signal available that actually indicates the data rate of the incoming SD-SDI signal is the 27 MHz rx_ce_out output of the UHD-SDI wrapper.
For some video applications, particularly those that do not need to retransmit the recovered video over an SDI interface, the rx_ce_out signal might be sufficient as a recovered clock.
Typically, this signal is used as a clock enable to downstream modules that are clocked with the rxoutclk from the GTX receiver. This is how the UHD-SDI datapath in the UHD-SDI core works - using the rx_ce_out signal as a clock enable. If an actual 27 MHz recovered SD-SDI clock is required, there are several options that can be used to generate one. Refer to Implementing SMPTE SDI Interfaces with Kintex 7 GTX Transceivers (XAPP592) for more details.