I think there will be a small latency created by not having the temp sensor in the flow path, should be minimal though. The oil that sits around the sensor will tend to be static and instead will get heated and cooled by the oil around it. Worst case maybe 10 seconds? I don't see that as a big issue.

is there not a fitting that is just a straight female to male adapter?

There is yes.
1/8 NPT Female to 1/8 NPT Male Extension [FITT012] - $4.00 : Palmers Pursuit Shop, Where Custom Still Means Something

nice I'd rather use that,

I like the 90 for the simple fact that it keeps the sensor cable tight to the oil cooler lines.

I like the tee better for the simple fact that the sensor is better exposed to the oil.