Yes, Russians will understand you, but that kind of pronunciation will sound hyper-correct. It will sound like you're spelling the words instead of pronouncing them.
Some Russian dialects exhibit a phenomenon known as "okanye" (оканье), whereby unstressed о and а beare pronounced differently. You may sound like a speaker of one of those dialects.
The Russian rendition of Church Slavonic also forbids vowel reduction, so a person speaking with that kind of pronunciation may resemble a priest reciting a Church Slavonic text to a Russian speaker.