It's a genuine concern, and the short answer is "sometimes, which is why you shop around." The worry is the classic subsidy dynamic: wherever a grant or a tax break exists, there's a temptation for prices to drift up to absorb it, so the customer doesn't see the full benefit. It's arguable that the 0% VAT in particular became margin for installers in places rather than a clean price cut, and that hardware should carry only a modest markup over wholesale but often doesn't.
There are ideas for fixing this, such as SEAI setting approved cost ranges for each component, or zero-interest loans instead of grants so repayments come from the bill savings. Those aren't the system we have, though. What you can do today is treat the grant as your saving, not the installer's, and verify it. Use the published rule (about €2,500 + €500 per kWp + €250 per kWh of battery, after the grant, for value kit; see asksolar.ie/method) as a yardstick, get three like-for-like quotes, and be suspicious of any "rewards scheme" or padded extras that conveniently equal the grant amount.
The market is competitive enough that good installers do pass the savings on — on the published rule a basic 4 kWp panels-only system comes to about €4,500 after the grant. If a quote seems to have quietly inflated to swallow the grant, comparing it spec-for-spec against others usually exposes it. The grant and VAT relief are real savings; making sure they land in your pocket rather than the installer's is just a matter of doing the comparison.