Is this quark gluon fusion and if not, what would qg fusion look like?
"fusion" is not a terminology appropriate for bound states. One would not call the hydrogen atom an electron proton fusion. Bound states are quantum mechanical states with discreet energy levels. You could name any scattering of a quark with a gluon as fusion, as long it is not modeled as a bound state.
If one wants to search for bound states of quarks and gluons, as they are doing in the paper by CMS , (the proposal of the search here).
An excited bottom quark, b∗, is used as a benchmark model when setting limits on the cross section for a heavy resonance decaying to a top quark and a W boson. The hypotheses of b∗ quarks with left-handed, right-handed, and vector-like chirality are excluded at 95% confidence level for masses below 2.6, 2.8, and 3.1 TeV, respectively.
The resonance will be seen in the decay products and will have a unique mass and quantum numbers depending on the quantum numbers of the particles it decays to.
is there a reason a down quark wouldn't work?
For the specific in the quote above a b quark is needed in order to model a quark bound state that would decay to a top and a W of a specific mass. One has to know the specific bound state proposed in your link to see if the same outgoing particles would be derivable from a bound d. For the diagram you show a d would do as well.