Even at max power on the 225 (18dBm per chain or 23dBm 3x3 MRC, ignoring antenna gain), if you lose 6 due to connectors and cabling, you're now at 12dBm per chain or 17dBm 3x3 MRC, ignoring antenna gain). In addition to Tx loss, remember you lose that on the Rx side as well (your AP becomes 5-6dB more deaf). So both Tx range and Rx range decrease, regardless of what you do with the power. With a 275, we have 23dBm per chain, or 28dBm from the radio (ignoring antenna gain) and no RF losses. You can do the math on how much farther clients can hear and talk back to an AP when there's a 10dB difference.
Ventev/Terrawave products should be fine. Any M-to-M extension cabels would have to have a coupler between them, worth two connector pairs, which means more loss.
You still want every connector on an AP terminated, at least for the MRC gain (on the 3rd chain worth ~1.5dB). So you want to use three ANT-19s. Also, how are they planning on mounting the three ANT-19s? If wall mounted, they will have to build a standoff to get them away from a wall 6-18" ideally, and then some kind of proper separation distance between them as well. All that money they *think* they are saving by using an indoor AP is going to be spent on time and labor and materials costs trying to make the indoor AP.outdoor antenna solution work, when they could just do a simple AP-275 on the wall and be done.
Note they have to buy THREE lightning arrestors, not just one. and three of every cable they chose to extend. The cables and arrestors will be hundreds of dollars at least, and then the standofs and structs will be another couple hundred, and then 4-5x the time and labor costs. All of that for about 30% of the performance and range of a 275.