Is it normal to tap a tankless heater condensate line into the vent pipe above my ejector pump?

You're not overthinking it. That's a hack job on two counts. I had a tankless put in a few years back and the condensate line is one of those things that separates the guys who know the equipment from the guys who just know how to hang pipe. The condensate off a gas tankless is mildly acidic, and most manufacturer instructions are real clear that it needs to run through a neutralizer before it hits any drain, doubly so on a septic system since that acidity can mess with the bacteria in your tank over time. No neutralizer on a septic setup is a legit problem, not a nitpick.

The connection itself is wrong too. You don't drill a hole in a drain line and shove a tube in with goop. That sealant will soften and fail eventually, and even if it held forever, the bigger issue is that condensate needs an indirect connection. That usually means a small air gap, so the condensate drips into a standpipe or receptor rather than being glued into the drain itself. It also typically needs its own trap so sewer gas doesn't come back up that little tube. A hole with caulk gives you none of that. And tying it in right above an ejector basin, where the line is open to the pit, makes it even sloppier.

When you call, ask for the service manager, not whoever answers the phone. Tell them the install doesn't match the manufacturer's installation manual on two points, the condensate discharge and the neutralizer, and that you want it corrected to code. Those manuals are usually available online as PDFs, so pull up your model's and have it in front of you. Companies that did the work themselves know exactly what a code complaint means, and a reputable outfit will come back and fix it under warranty. If they push back, that tells you what kind of outfit you actually hired.

Before the call, verify the unit acutally produces condensate in the first place, because only a condensing model does, and a non-condensing tankless has no acidic condensate line to worry about at all. The model number is on a sticker on the side of the heater, and the spec sheet will say wich type it is. If yours turns out to be condensing, which it almost certainly is if there's a tube dripping water, then everything the previous poster said applies. Either way, snap a few photos of that drilled connection from a couple angles before anyone touches it, since installers have been known to quietly redo things and claim it was never done differently.

One more thing to add to your call list: if they do come back and put a neutralizer on, ask them how often the media needs replacing. Mine was installed with a little cartridge full of limestone chips and the manual said to check it every six months. Nobody told me that at install and by year two the stuff was basially spent, just sitting there looking official while acidic water ran right thru it. Also worth asking wheather they sized it for a condensing unit, because the little inline ones are not all the same and some are meant for a furnace, not a tankless pushing way more condensate.

Seen that hole-and-goop trick more times than I care to remember. Back when I was learning the trade, we ran condensate into a laundry sink or a little crock with a pump if gravity wouldn't do it. Simple, easy to service. Even a plain standpipe was better than gluing a tube into a fitting someone drilled by hand, because that hole takes real bite out of the pipe wall and it's the kind of spot that splits down the road. While you're poking around up there, check whether the tube sags anywhere. If water can pool in a low spot it'll eventually plug up with crud and back up into the heater itself.

Agree with the guy who said that drilled hole takes a real bite out of the pipe wall. When I had a similar setup corrected, the plumber wouldn't even try to patch it, he just cut out the whole section with the hole and put in a new fitting with a proper barbed adapter for the tubing. Cost me maybe twenty bucks in parts and it's been fine for years. Might be worth mentioning to the OP so they know a full replacement of that pipe section is a fair ask, not an upsell.