Boosts and stances yes, strikes and counters no—mostly.
Stances are semi-permanent, passive effects. As long as you are in one, they benefit you the entire time. Boosts are temporary bonuses applied as a swift action, usually only lasting that round. Many of each improve your attacks in some way, and that would include the attacks in spell combat and the attack made during spellstrike.
But strikes require standard actions or full-round actions, so there is a conflict there: spell combat itself requires its own, separate full-round action. You can only use one or the other at a time.
Spellstrike is not a separate action, but it replaces the touch attack made during a spell with a weapon attack: it does not give you another standard action or full-round action with which to use a strike to deliver that spell.
And counters are right out, being immediate actions that occur outside your turn.
The one exception is if you cast a touch-attack spell and hold the charge (either by not taking the free attack, missing the free attack, or by using a spell like chill touch that allows multiple touches). In this case, future weapon attacks—including those made as part of strikes or counters—could deliver the touch. This isn’t usually all that helpful—after all, you could have already hit with the spell by the time you can deliver it with a strike—but it is useful in the case of misses or things like chill touch.
But that’s such a niche use that, unless you plan on focusing on a multi-touch spell like that anyway, it’s not a good enough reason to use Martial Training to get strikes. Boosts, counters, and stances will be your way to go.
Disclaimer: I have done free-lance work for Dreamscarred Press, but I did not work on Path of War or Path of War: Expanded. My answer is based on my reading of the rules and my memory of conversations with those who did work on it.
