It won't work with the switch,
Out of curiosity, is there any switch that is officially supported to use with a DPH LNB? I know a couple of members reported success using a DPH42 switch with a DPH LNB. However, the official supported solution (in the DPH42 instructions) is to only use DPP LNB's with the DPH42.
but it will with the Wally. You will just only have 1 tuner if I remember correctly.
If I remember correctly, an unmodified Wally will still tie up two tuners out of the total 16 tuners available with a DPH LNB (or two of the 32 tuners available with a DPH42 switch). There is a special code that Dish can place on the account for MDU or commercial accounts, if they want more Wally receivers connected to a single dish and/or switch, that makes each Wally single-tuner. On the Diagnostics screen, the model listed will change to Wally T (or Wally COMM T) when this code is applied.
I've done VIP to Hopper upgrades, swapped the LNB and went into the house where the old receiver - a 211, 722, etc was back on live TV, but the Dual Tuners, TV2 wasn't operating any longer with the DPH LNBF.
You didn't mention whether you did the Check Switch on the old receiver. I know that the customer probably wouldn't want you wasting your time trying to get the old receiver working, since they are upgrading anyway. However, I was thinking that since you swapped the LNB, a Check Switch may still be necessary to get the old receiver to recognize the new LNB for both tuners. If it still doesn't work after the Check Switch, then it could just be a case of the separator being incompatible with the DPH LNB. That still would not rule out the possibility of two cables directly from the DPH LNB to the dual-tuner receiver (without using a separator) working properly. It may be a fun experiment for someone who has the equipment and the time to try it.