Not quite sure what you mean with your push-ups example?
Isometric training is a form of static training eg. pushing against an immovable object, where there is no movement of the joints during the period of exertion. ie. the length of the muscle(s) being worked does not change.
Static-holds with dbs or a bb would be an example of isometric training. Good for grip strength which might help with all types of deads, chins, rows etc.
You could definitely incorporate isometrics within an HST cycle (but when possible, negatives would be better for hypertrophy). They would probably be best used towards the end of a cycle because it is possible to generate high tension with an isometric contraction (you can isometrically contract against a heavier load than you can concentrically contract against it). The downside to isometrics is that they tend to produce a strengthening effect only in the joint angle that is being trained. That works out just fine in the case of static-holds, as gripping a bar with the hands closed is exactly the position you want to strengthen.
To use static holds in an HST cycle you could use time and load as variables to work with for a progression; each time you did them you could add more load and/or try for more total time holding onto the bar.
As far as rehabbing tendons goes:there is some research on using eccentrics for rehab'ing weak or injured tendons:
http://ajs.sagepub.com/content/26/3/360.abstract
I tried eccentrics for a forearm/elbow tendon injury. It did seem to help speed recovery compared to everything else I had tried. Not very scientific, I know.