In short, no, it's not possible to check the fuel the conventional way, ie. with a dipstick. I used to fly a R2160. I had concerns about the reliability of the fuel gauge also at the time. Reason was that due to weight limitations while doing aeros. Anyway, the concerns I raised to the company were the following:
1. The fuel gauges are calibrated in units of 0,1,2,3 etc where each number corresponded to a given amount of fuel and the interpolation between the numbers isn't linear.
2. The fuel indicator 'needle' is pretty thick and is actually about a quarter the thickness between units.