A: The way you worded your question, I had to laugh. You don't ask if straight men get lower back tattoos - you ask if men can get lower back tattoos and be straight. Like if a straight gay got a lower back tattoo, it would suddenly make him gay.
The good news is, getting a lower back tattoo will not change your sexual orientation. However, I wouldn't say "a lot" of straight men have lumbar tattoos - it is more commonly found on women. But that doesn't mean men don't, or can't. If you want it, the only thing holding you back is you. While it's possible that a stranger may question your sexuality if they happen to notice the tattoo, who cares? Your friends and family obviously know who you are, and (hopefully!) you know who you are, so quit worrying about what other people think. If you're really worried about how "manly" you are, then get some cahones and do what you want!