Is using a primer just over the glazing absolutely neccesarry? I'm only painting the house due to the nails being driven too deep. I don't want to take the chance of water getting into the siding. Was just planning on painting directly over the whatever it is I decide to use. Thanks.
So, you were thinking of just filling in the nail holes and painting over them.
You WILL have the same "adhesion" (if you want to call it that) between glazing putty any any "oil based" product, be it an exterior alkyd primer or an exterior alkyd paint.
But, you have to keep in mind that the ability of your paint to hide an underlying colour depends on several factors, including the colour of the paint (which is determined by pigments in your paint) and the gloss level of your paint (which is also determined entirely by the pigments in the paint). So, if you're wanting to paint over glazing putty with a high gloss organic colour like Navy Blue, Hunter Green, Blood Red or Canary Yellow, you may need several coats of paint to hide the light grey spot of glazing putty underneath.
The reason why it's common to see people priming over a wall with a tinted primer is because primers are white, so good quality primers will have a lot of titanium dioxide (the highest hiding white pigment) in them, and that allows one coat of a high hiding primer to hide better than several coats of some paints.
Also, primers (both latex and oil based) are made using binders that are chosen for their superior adhesion to common substrates, whereas the binders in paints are chosen based on how hard a film they dry to. You want good adhesion in your primer and you want your paint to form a hard film because the harder the paint film, the more scrubbing it'll stand up to without losing it's gloss, the less of a mark furniture rubbing against it will make, the less of a mark scratches will leave behind and so the longer the paint will stay looking good. The softer the paint film, the more easily it will be damaged by wear and tear, and the sooner it'll start looking like it needs a new coat of paint.
So, if you use glazing putty to fill the nail holes. BOTH an oil based primer and an oil based paint will stick to it like chewing gum to the underside of a church pew. So, you don't really need to use a primer to get good adhesion to glazing putty just cuz of the crosslinking between the putty and either alkyd primer or alkyd paint.
I'd say your best bet is to try one nail hole. Paint over it with the paint you intend to use and see if it hides the underlying spot of putty well. If so, then do the rest of your nails the same way. If you can see the putty spot through the dry paint, and that bugs the he11 out of you, post again.