I thought secondary PTSD was about being exposed to the primary sufferer's symptoms.
From what I've read, there are a lot of issues and/or disagreement over the labels, especially since none of them are official diagnoses.
Like, Secondary Traumatic Stress Disorder supposedly comes from indirect exposure to a loved one's trauma experience (ie hearing their firsthand experiences in detail) and reacting to it with symptoms that parallel PTSD, like hypervigilance, nightmares etc. It would be like knowing your spouse had a specific trauma, and because of it, he has "trigger X." You then start to be hypervigilant about avoiding "trigger X" to protect your spouse, but then eventually "trigger X" begins to trigger you and you "relive" your sufferers trauma if you experience that trigger too. Its pretty controversial, since it's more of a reaction than a disorder.
I think the stress from dealing with your sufferers symptoms is more of a Compassion Fatigue. This would be more along the lines of dealing with the push/pull, being the target of lashing out behaviors, etc.
I'm pretty sure that living with a PTSD sufferer that is abusive because of their symptoms (like in domestic violence situations) would just cause another case of PTSD in the supporter if they go through their own trauma.
"Secondary PTSD" seems to be a blanket term that is applied to any or all of these, depending on where you see it.