Yes they will no point promising someone DPORK if you cannot win it.
Ruto has make sure he has rigging margins - given Uhuru will try to rig.
I think for both Raila and Ruto GEMA DPORK is ideal.
However if Raila has picked Kalonzo and Uhuru lead the Kabila mbili propaganda (azimio unity aint working) -
Ruto has the leeway to pick maDVD
I agree with you, what Mudavadi brings is respectability of the ticket more than numbers. I still feel that DP has already consolidated all that he can from Central, bypassing Uhuru. If Azimio candidate was anybody else, I agree Ruto's running mate would matter but in this case with Raila's candidacy, DP's GEMA votes are safe. Any GEMA running mate has has the same issue in my opinion, they are not adding much to Ruto's basket. And they are probably not going to leave for Azimio (I'm not sure about Meru though).
It will also avoid that talk of Mt Kenya and Kalenjin which usually tends to suppress support in other regions.
But anyway we're just armchair analysts, I'm sure they are looking at all those scenarios and will act accordingly. Plus I think all these issues will be properly negotiated so nobody feels shortchanged. Ruto has the advantage that he has yet to betray anyone politically so far, so his word is more trustworthy.