Circular polarization does work to make RF cut through difficult areas. I have not seen any commercially made circularly polarized antennas for UHF, but I can say that almost EVERY radio station on the VHF broadcast band (FM 88-108MHz) uses a cycloid, or other type of circularly polarized antenna system. The science is well proven for transmitting. The question would be: Can they receive as well?
You are asking the same question that this entire topic is about, I have also provided an answer to your question and here it is again. Echolink is HAM, this is GMRS. Most of the HAM linking systems are based on Asterisk using the Allstar network. Asterisk is the same system that is being used to link GMRS repeaters using the network here at MyGMRS or one of the other GMRS networks that has been set up. Some allow simplex nodes some don't. The MyGMRS network is repeaters as they are more useful. I would suggest you go back an read whats already been posted as your question has been answered already. As well this forum has a topic dedicated to just this... Below is the link you could have found by reading my other post or simply using the forums search box at the top of the page. I don't mind helping or answering anybody's questions so long as you first attempt to find the information on your own. Answering the same questions over and over because people don't want to take the time to look is annoying and a big turnoff.