Short answer: Of course!
Many angel groups require you to submit through Gust because it offers a consistency and makes reviewing applications easier. But not all use Gust same as not all use AngelList... I haven't met an angel who frowns upon using multiple platforms.
I would encourage you to leverage your twitter and Facebook or Instagram to meet angels and get in their radar (don't hassle or stalk) just try to get exposed a bit to them by being part of the same meetup group, follow the same blog, membership... Subscribe to their own blog.. And when you submit funding request considerations do please send a follow up email or a call or basket of fruits if you have contact them before.
You can use multiple services as has been answered already, but I would suggest that using multiple services can create a "negative signal" by investors. Also, the likelihood that you will get *any* inbound interest from AngelList without already having "high signal" investors or an active syndicate is very low.
So I would suggest that you focus on whatever is going to give you the highest level of support and service. I recently spoke to the WeFund guys who are still actively curating what gets listed to their investors. I think if you don't have a network of investors, these smaller networks are a good starting point.
I've helped a lot of entrepreneurs here on Clarity with their early-stage fundraising questions (read my reviews). I'd be happy to talk to you to learn more about the specifics of your situation and give you advice based on my understanding of where you're at.
AngelList is only one among many, online and offline platforms. It makes sense to pitch your deal where there is a ready market for your proposition. Neither AngelList nor Gust has the market reach of Indiegogo or Kickstarter due to the delay of the JOBS Act Title III which give SMEs access to non-accredited investors. Unlike CircleUp or FundersClub, AngelList or Gust does not curate its deal flows.
I could tell you more. Take advantage of the interim free call.
Stick to one and hopefully to the one that is the leader, you can actually verify which one it is ( http://www.similarweb.com/website/angel.co?competitors=gust.com ). Fundraising consumes time, you could be at it 1 month 6 months or even a year so I recommend sticking to one single platform. It tends to be chaotic once you are 2 months in the process and you need to update multiple platforms, eventually one is going to lag behind because you will be so inmmerse in other activities. Also from a SEO perspective your top listing will benefit more when content is not replicated in other platforms, that way you dont dillute yourself and the power of achieving rankings for "long tail"
As of today more investors "gravitate" today in Angel List than in other platforms.
It's important to know the players in the space and what they're good at.
AngelList - very tough to raise funding and connect with people. There is a lot of saturation and barriers to connect (you need to have them following you or get intros from existing connections).
LinkedIn - work on your profile, post regulatory and garner support for your posts to position yourself as a thought leader whilst giving interesting status updates on your business. You can search LinkedIn through the "advanced" search tool to find angels in your city. Connect with a few, ask for advice and to meet for coffee. If they like you, they will help and usually know other angels. Strike for Angels who know the market problem.
SeedInvest - all the investments need to pass the screening committee and the partners. Thereafter there is some heavy due dill whence from the team and CrowdCheck. Only a handful of vetted deals are available and they co-promote to their investor pool. If it's a really good deal they may back the deal with $200k of SeedInvest's own capital once you pass $250k in fundraising. NOTE: they're a registered broker-dealer. They take 6.5% of capital raised but all the investors are accredited.
There is also OurCrowd, Crowdfunder, SeedEquity... It also depends where you are in the world as in the UK, there are some amazing tax-breaks for Angels and VCs.
Hit me up if you want to chat a bit more about it.
There's some overlap between the two groups of investors but not as much as you might think. You can basically use the same information to keep both platforms updated and reach 30-40% more investors — why wouldn't you want to do that?