My company uses Concur for the travel portal and the corporate travel agent is CWT. Booking.com and Hotels.com rates are displayed interspersed along with the rates offered by Marriott directly. In general the booking.com and hotels.com rates are the same as the Marriott rate. So booking those rates doesn't reduce expenses nor am I aware of any backend rebate to my company for using the OTA's. So I suspect either Concur and/or CWT are somehow getting a commission or other rebate from the OTA's. Otherwise, why would they even be listed? Anyway, as other posters have already noted, carefully check the rates in your travel portal to avoid OTA bookings. I have never used the TravelPerk portal but imagine it would be similar to Concur with OTA rates interspersed with direct Marriott rates. Good luck and YMMV....

--Jon